When American bomb makers began visiting China in 1979, they were startled by increasingly pointed questions that suggested their Chinese peers were hot on the trail of the secret to building a modern nuclear arsenal. It allows hydrogen bombs to be made so small that many can fit atop a single missile or be fired from trucks, submarines and other mobile platforms.
China succeeded on Sept. 25, 1992, the news coming from a spy who told his American handlers that Beijing had exploded a bomb based on the miniaturization secret.
A team of scientists at the Los Alamos weapons laboratory in New Mexico set to work on a whodunit with huge implications: Was China's advance the result of espionage, hard work or some mix of the two?
Today, the debate rages on. Experts agree that spying occurred, but clash violently on how much was stolen and what impact it had on Beijing's advance, if any.
The Los Alamos team concluded in 1995 that China's stride was probably based on espionage. A report this year by a Congressional committee that made the case public went further, claiming that it would have been ''virtually impossible'' for China to have made small warheads ''without the nuclear secrets stolen from the United States.''
Continue reading the main storyThe Congressional report unleashed criticism from scientists inside and outside the Government who said the importance of the espionage was overstated, and that China could well have achieved the breakthrough on its own, as it insists publicly.
A review of the dispute, based on months of interviews and disclosures of weapons and intelligence secrets, suggests that the Congressional report went beyond the evidence in asserting that stolen secrets were the main reason for China's breakthrough.
The review also bolsters a point of emerging agreement among feuding experts: that the Federal investigation focused too soon on the Los Alamos National Laboratory and one worker there, Wen Ho Lee, who was fired for security violations. The lost secrets, it now appears, were available to hundreds and perhaps thousands of individuals scattered throughout the nation's arms complex.
Federal officials asked in recent days that some details about weapons design and intelligence sources not be published, and The New York Times agreed to withhold them.
For the Los Alamos team of detectives, the overall spy theory was supported strongly in 1995 when the Central Intelligence Agency obtained an internal Chinese document that included a description of the United States' most advanced miniature warhead, the W-88. Revealing for the first time their top evidence in the case, the document's secret contents, Federal officials say the Chinese text cited five key attributes of the warhead, including two measurements accurate to within four-hundredths of an inch.
But the critics, who are also revealing new information, insist that Beijing, even if it spied, made the miniaturization breakthrough on its own, pursuing it for at least 13 years, from 1979 to 1992.
The prowess of Chinese scientists, American experts said, is suggested by a camera they built for photographing nuclear blasts, which was far better than a similar one made by the United States.
''They don't need any help from us,'' said Harold Agnew, a past Los Alamos director, visitor to China and Federal intelligence adviser. ''They're just curious, as we are curious about them.''
Deconstructing the damage wrought by espionage is an imprecise art that mixes inference, evidence and deduction. In the vacuum between what is known and what is suspected, personal, partisan or institutional bias often rushes in.
The debate over Chinese spying has been blurred by issues that include Republican distaste for President Clinton's China policy, accusations of racial bias in the investigation and fears among scientists that the uproar is prompting security measures so tight as to damage work, morale and recruitment.
As in most spy cases, the evidence is open to interpretation. Several critics familiar with the Chinese document obtained by the C.I.A. said that its description of the American warhead was not by itself sufficient to build a miniaturized warhead.
The Energy Department official who supervised the Los Alamos inquiry, Notra Trulock, agreed with this assessment but said the information was secret and had never been mentioned in any public document or Internet posting. Anyone who had it, he and his team reasoned, must have also obtained access to a much broader range of secrets about the warhead's design.
In addition, Mr. Trulock said in an interview, knowing the approximate size and shape of the components provided a road map to Chinese bomb makers, probably allowing them to skip years of preliminary testing.
Mr. Trulock added, however, that the Congressional committee was too categorical in its report, which was based in part on his testimony.
''When I testified, I used the appropriate caveats to express uncertainties in our evidence and our conclusions,'' said Mr. Trulock, formerly the Energy Department's intelligence chief. ''We typically said: 'Probably this. Probably that.' '' The committee, he said, ''made judgments'' about the centrality of spying in China's breakthrough.
Representative Christopher Cox, a California Republican who was chairman of the committee, defended the work of his staff of 47, which included no one with nuclear design experience. The panel, he said in a lengthy interview, drew largely on Clinton Administration witnesses for its expertise. The conclusion that espionage allowed Beijing to skip decades of research, he said, was an appropriate one, based on the Government's own evidence.
''Judgment matters,'' he said, responding to Mr. Trulock's criticism. ''We don't know everything to a certainty. The question is what is more likely than not.''
In the interview, Mr. Cox expressed surprise when told of the depth and breadth of China's interest in the miniaturization secret. He also played down the idea, cited by Federal skeptics of Chinese spying, that most of the world's nuclear powers have figured out the secret of miniaturization.
Can China, Mr. Cox asked, ''develop it indigenously because France did? That is a stretch. It's almost apples and oranges.''
The Secret
America Shrinks An Atomic Match
From the dawn of the nuclear age, miniaturization has been an obsession of weapons designers. The world's first atomic bomb, designed by the Los Alamos laboratory and detonated in the New Mexico desert in July 1945, was an awesome but cumbersome affair. A lump of plutonium the size of a softball was surrounded by a much larger ball of high explosives that was five feet wide and made up of 32 explosive charges and 64 detonators. Big as a car, it could not have fit into a small airplane, let alone a missile.
In 1952, American physicists made an important breakthrough: the H-bomb. Roughly a thousand times more powerful than the first atomic weapon, the hydrogen bomb was a two-stage device. Inside its dense casing, an atomic explosion -- called the primary -- worked as a match to kindle an even more powerful detonation by the bomb's hydrogen fuel, which was known as the secondary.
Size was an issue from the start. The first hydrogen bomb stood two stories high and weighed 82 tons. It would be militarily useful only if it could be shrunk, and over the next few years, the country's best physicists set out to do just that. After considerable trial and error, they figured out that they could obtain the same kind of explosive power from a smaller package. A main breakthrough centered on the large, heavy atomic match. By shaping its plutonium fuel into an ovoid, roughly like a watermelon, scientists were able to drastically shrink the size and number of the explosives that triggered the nuclear blast.
After at least one flop, the radical idea roared to life in July 1957 in a nuclear explosion in the Nevada desert, according to Chuck Hansen, author of a detailed history of America's early nuclear efforts. It had taken the United States a little more than five years to move from the first hydrogen bomb to its miniaturized cousin.
The development had profound implications for the cold war's nuclear competition.
Shrinking the atomic trigger from something roughly the size of a washing machine to something smaller than a football allowed weapons designers to put thermonuclear arms atop small missiles that could be launched from submarines or mobile platforms like trucks. Arms would no longer be confined to bombers or silos in the ground.
The advance meant weapons could now be carried, quite stealthily, closer to enemy shores and could be made safer from attack. It also meant warheads could fit into the cramped spaces of narrow nose cones, which streaked faster to Earth than blunter shapes and were less buffeted by winds during the fiery plunge, making them more accurate.
The first warhead in the new generation of weapons, the W-47, was less than half the size of the bomb that leveled Hiroshima but up to 80 times more powerful. In 1960, when the first Polaris submarine put to sea, each of its 16 missiles was armed with a W-47.
The weapons continued to evolve, and by all accounts, the apex was reached in the 1980's with the W-88, one of the most deadly weapons in the American arsenal.
The warhead, made for submarines, first went to sea a decade ago and is considered quite powerful for its small size. The precise size is secret. But at least eight W-88's can fit atop the Trident D-5 missile, which is less than seven feet wide. Since Trident subs have 24 missiles, a single submarine can carry up to 192 of the thermonuclear arms.
Today, American submarines on patrol in the Atlantic carry the small warheads. And the Navy is adding them to its Pacific fleet, so in the next few years the W-88 is likely to be aimed at China.
The Chinese
Late to Start, Quick to Excel
China was late in joining the nuclear club, but showed considerable skill when it did.
Beijing detonated its first bomb in 1964. The tricky design was based on uranium, like the Hiroshima bomb, but saved costly fuel and made the bomb lighter, increasing its military value.
Sidney D. Drell, a Stanford physicist and Clinton Administration adviser, writing in ''China Builds the Bomb'' (Stanford University Press, 1988), called the feat ''enormously impressive.'' Beijing's first hydrogen bomb came just 32 months later.
By comparison, the step from nuclear to thermonuclear took London 66 months, Moscow 75 months, Washington 87 months and Paris 103 months, said Robert S. Norris of the Natural Resources Defense Council, a private group in Washington that monitors nuclear arms.
China set off just 6 test blasts to get to the H-bomb stage, versus 31 for the United States. The low number was typical. While developing at least six types of weapons, Beijing over the decades conducted relatively few nuclear tests, 45 in all, versus 1,030 for the United States.
The evidence strongly suggests that China, in its first phases of missile building, had no idea how to shrink thermonuclear arms. According to ''China's Strategic Seapower'' (Stanford University Press, 1994), the warhead for the submarine missile deployed by Beijing in the 1970's weighed 1,300 pounds, more than twice the old American W-47, suggesting that the Chinese were still using a spherical atomic match to ignite hydrogen bombs.
China's land force was modest. Starting in the 1980's, it deployed about 20 missiles that can now reach anywhere in North America, each topped by a single warhead that can unleash a force equivalent to up to five million tons of high explosives. That is about 300 times stronger than the Hiroshima bomb.
The big warheads are not particularly accurate, but they fit China's professed war doctrine -- to fire nuclear arms only in retaliation. The big missiles can, if necessary, hit a city.
China's interest in building smaller weapons was spurred, in part, by the United States' development in the late 1970's of a high-accuracy design known as the Missile Experimental, or MX, that bristled with 10 warheads. Though meant primarily to unnerve Moscow, the weapon also worried Beijing, which quickly grasped that its handful of big land-based missiles looked like sitting ducks that could be destroyed in a first strike of precisely aimed hydrogen bombs.
Beijing's unease grew as the American Navy in the late 1970's unveiled plans for a new submarine-launched missile nearly as unerring as the MX and bearing an even more powerful warhead -- the W-88.
American intelligence agencies knew little about China's nuclear program and modernization plans, if any, before President Richard Nixon's visit to China in 1972. But the military ties that followed the Nixon diplomatic initiative opened the door.
By 1979, American nuclear arms designers and security experts were starting to visit their Chinese peers, weapons labs and Lop Nur, the sprawling site in China's western desert where prototype nuclear weapons were detonated.
From Los Alamos alone, at least 85 scientists and officials made trips from 1979 to 1990, according to Robert S. Vrooman, a former C.I.A. officer who at the time directed counterintelligence at Los Alamos.
Top visitors included Dr. Agnew, the past director of the weapons lab; Danny B. Stillman, its head of intelligence; and George A. Keyworth 2d, a physicist who later became President Reagan's science adviser.
The benefits were judged to far outweigh the risks that arms scientists in informal settings and conversations might, by accident or design, give away secrets. And indeed, the Americans learned much.
''This was a huge intelligence game for the United States,'' said a United States official who spoke on the condition of anonymity. ''At the beginning we knew zip about China.''
One discovery was that parts of the Chinese program were quite advanced, including technologies for bomb development.
''They have excellent facilities, some better than ours,'' said Dr. Agnew, who in 1979 and 1982 was among the first visitors.
For instance, he said, the Chinese were able to peer into fiery blasts with an advanced camera known as pinex, revealing details to aid warhead development.
The American version of the device had one axis, he said, the Chinese version two, doubling its usefulness. ''It's much better,'' Dr. Agnew said.
The American visitors also learned much about what China lacked. From a barrage of inquiries over the years, it became clear that Beijing was eager to learn everything it could about shrinking the atomic trigger. The questions were regular, increasingly pointed and never answered, American officials said, insisting that Beijing got no secrets that way.
But in one case, investigators became suspicious about an American scientist at the Livermore weapons lab in California who in 1979 had talked with Chinese scientists.
The suspect, born in Taiwan, never confessed. But some Federal investigators, in an investigation code-named Tiger Trap, feared the scientist had compromised not only the design of the W-70, a neutron bomb, but the secret to making small atomic triggers.
Weapons experts say that the crucial insight of the watermelon shape can be communicated with a few comments, a hand motion or a simple drawing on the back of an envelope, although years of computing, calculation, experiment and factory labor are then needed to turn the idea into nuclear blasts.
''The real challenge is not in the design, it's in the manufacturing,'' said Houston T. Hawkins, head of international security studies at Los Alamos. For example, he said, plutonium, one of the most complex metals known to science, is difficult to cast because of its odd ways of reacting with other metals and materials. ''It's a strange beast,'' he said of the dense metal that fuels most atom bombs.
The Breakthrough
China Takes Giant Nuclear Step
China finally succeeded in exploding a miniaturized bomb on Sept. 25, 1992, American officials revealed. It took intelligence analysts more than two years to fully understand what China had accomplished, its feat becoming clear only after a Chinese nuclear expert who had been recruited to spy for the United States delivered an intriguing report to his American handlers.
The spy said that China's September test blast, initially viewed by American analysts as routine, was anything but. The bomb detonated that day was miniaturized with a core, the spy said, in the distinctive shape of an ovoid, indicating China had begun to master the art of making modern warheads.
In the mid-1990's, the task of tracking the technical ins and outs of other nations' nuclear programs fell to the national weapons labs. Among the sleuths was Dr. Robert M. Henson, an experienced weapons designer at Los Alamos who had been analyzing intelligence on foreign programs since 1988.
In January 1995, Dr. Henson said in an interview, he began looking more closely at how China had solved the miniaturization puzzle. For help he turned to Lawrence A. Booth, a friend who specialized in Russian analyses.
''We kept looking into it for two weeks,'' Dr. Henson recalled. ''Then, we decided to do something.''
They drew up their analysis and eventually took it to Mr. Trulock, who the previous year had become director of intelligence at the Energy Department, which oversees Los Alamos. Mr. Trulock, who has a bachelor's degree in political science and no formal technical training, said he wanted to bring in other nuclear experts, particularly ones who had long experience in developing the miniaturized nuclear triggers for hydrogen bombs. John L. Richter of Los Alamos, a scientist who filled that void, joined the team.
The group looked more closely at a clue provided by the Chinese spy, who described the size of the bomb's atomic core with an analogy to a common household object, officials said in a new disclosure. Working from that, the scientists calculated a more precise size and Dr. Henson and Dr. Richter went through the American stockpile of nuclear arms, looking up measurements to see if any matched.
The atomic trigger of the W-88, they discovered, was close enough in size to raise suspicions.
The Energy Department held meetings in which the Los Alamos team was joined by analysts from the C.I.A. and the Defense Intelligence Agency. Federal officials now say the intelligence agencies were skeptical, reasoning that too much was being made of a foreigner's rough analogy. But the Energy Department and the Los Alamos team felt the evidence was provocative.
The breakthrough came in 1995, as has been previously disclosed, when a Chinese Government official sent a package of secret Chinese documents to American officials.
Mr. Trulock said the most revealing document, dated 1988, laid out China's nuclear modernization plans for Beijing's First Ministry of Machine Building, which, among other things, made missiles and nose cones. It not only described China's plans but compared them to the nuclear arms of the American arsenal.
Relatively crude hand drawings sketched out the nose cones enveloping the W-88, the W-87, the W-78, the W-76, the W-62 and the W-56 -- warheads of the Trident, MX and Minuteman missiles -- and also gave their overall weights and dimensions.
In itself, these were not damning. Though still officially classified secret in some cases, such information by then was widely available in many unclassified American papers and articles.
But the Chinese document, some 20 pages in translation, went on to give sensitive data about the W-88, Federal officials revealed. It accurately described the shape of the atomic trigger as not spherical and said it was situated in the nose cone's narrow forward end -- an arrangement used in some but not all American warheads. And it correctly described the hydrogen fuel, or secondary, as having a spherical shape.
More unsettling to the team, it described the width of the casing that surrounds the atomic trigger to within a millimeter, or four-hundredths of an inch. ''That's pretty damn accurate,'' Mr. Trulock recalled.
A senior Federal official agreed. ''That opened eyes,'' he said. ''It seemed to confirm earlier assessments that had seemed insubstantial.''
Mr. Trulock said his team later found that the Chinese document gave a similarly exact measure for the width of the W-88's secondary, or hydrogen stage. ''Primaries are the long pole in the tent,'' he said, referring to the importance of the atomic trigger. ''But that measurement was as good as the one for the primary.''
The C.I.A. eventually concluded that the agent who sent the documents was acting under the instruction of Chinese intelligence. No one has ever come up with a persuasive explanation of why China sent the documents to American spies.
From 1992 to 1996, American officials revealed, China used its new atomic match to ignite a variety of hydrogen bombs, including one similar in some respects to the W-88. After this series of blasts shook the ground at the Lop Nur test site, China signed the Comprehensive Test Ban Treaty, signaling an end to its nuclear experimentation.
The Investigation
Federal Sleuths Hunt for a Spy
The Energy Department opened an investigation into the possible theft of W-88 secrets on Sept. 28, 1995, and over the next three years, Federal officials quietly tried to find out whether there was a Chinese spy in their midst.
If espionage occurred, Mr. Trulock and his team reasoned, it must have happened between 1984, when the warhead entered engineering development, and 1988, the date of the Chinese document.
Energy Department officials focused on Los Alamos, which had designed the bomb. They looked particularly closely at anyone who had traveled to China in those years or met visiting Chinese scientists.
Mr. Vrooman, then head of counterintelligence at Los Alamos and later a vocal critic of the inquiry, said investigators scrutinized only those people whose trips to China were paid for by the Energy Department.
Left unexamined, he said, were at least 15 additional people whose trips were paid for by the Chinese, the C.I.A., the Air Force or privately. These travelers tended to be top weapons designers and high officials -- the people who knew the most American arms secrets and had the most intimate contact with Chinese peers, Mr. Vrooman said.
In May 1996, the Energy Department turned over a list of a dozen suspects to the Federal Bureau of Investigation, which began a criminal case that eventually narrowed to Dr. Lee, an American scientist of Taiwanese birth working at Los Alamos.
Dr. Lee and his wife, Sylvia, had traveled to China in 1986 and 1988. Mrs. Lee was a secretary at Los Alamos who often met visiting Chinese delegations. And Dr. Lee, though a mechanical engineer by training and never a weapons designer, was familiar with the W-88 and many other nuclear arms and secrets (including the atomic trigger advance) because of his work on secret computer codes.
The F.B.I. believed it had enough evidence to seek a secret wiretap on Dr. Lee's phone calls, citing 20 reasons he was a prime suspect. But the Justice Department found the evidence unpersuasive and refused to seek a court order for the eavesdropping, a routine step in most spy cases.
Mr. Vrooman has charged that the inquiry was marred by a racist bias to target Chinese-Americans, an assertion Federal officials have vehemently denied. But the Republican chairman and the ranking Democrat of the Senate Governmental Affairs Committee, which investigated the spy case and heard testimony from Mr. Vrooman, concluded that Federal investigators had focused prematurely on Dr. Lee.
After the spy case became in public, Bill Richardson, the Secretary of Energy, recommended that Mr. Vrooman be disciplined for letting Dr. Lee have continuing access to secrets even after doubts about him had been raised.
Dr. Lee, fired this year from Los Alamos for security violations, including failing to report foreign contacts, has been charged with no crime and has denied any spying. After his ouster, investigators found that he had loaded many secret files onto an unsecured computer, raising the risk that they could have fallen into the wrong hands.
The inquiry most likely would not have come into public view had it not been for a series of unrelated disclosures about China.
In April 1998, The Times reported that two United States aerospace companies were under criminal investigation for providing rocket data to Chinese scientists.
A furor erupted in Congress. The House created a select committee, led by Mr. Cox, who had recently vied unsuccessfully for the House speakership, to look into whether the Administration's increasingly open policies on satellite exports had compromised national security.
There was no hint the committee would end up studying nuclear bombs. Composed of five Republicans and four Democrats, the committee did not learn of the suspected Chinese nuclear espionage until October 1998, just a few months before its mandate expired. On Nov. 12 and Dec. 16 it held secret hearings in which Mr. Trulock was called as the star witness.
In January, after three months of investigation, the committee completed a secret manuscript. In May, after a long argument with the White House over what could be made public, it released an 872-page report. The chapter on atomic espionage, just 37 pages, garnered most of the headlines.
In fiery prose accompanied by vivid color pictures and charts, the committee charged that Chinese spies had carried off vital secrets about seven of America's most advanced arms.
The People's Republic of China, it alleged, ''has stolen classified information on all of the United States' most advanced thermonuclear warheads,'' leaping from the clumsy designs of the 1950's to those that are far more modern and deadly.
The main evidence cited was the Chinese document obtained by the C.I.A. in 1995 and an inquiry in the 1980's into spying at the Livermore lab that concluded China had most likely obtained design secrets of the neutron bomb. The unclassified version of the committee's report gave no details of the 1995 document's secret details about the W-88.
The report was signed by the committee's four Democrats. But immediately after its release, Representative John M. Spratt Jr. of South Carolina, one of the Democrats, criticized it as rushed, superficial and exaggerated. The witnesses heard by the committee, he added, ''did not have the technical background to fully assess the nature or value of the information lost.''
The Debate
Analysts Sift For the Truth
Since then, Mr. Spratt's critique has been echoed and amplified by a range of top scientists and bomb designers who say Beijing could have miniaturized its warheads on its own without spying.
Richard L. Garwin, a physicist who has long advised Washington on nuclear arms, recently on a bipartisan team led by former Defense Secretary Donald H. Rumsfeld, said, ''there is no reason to believe that China could not have built perfectly adequate warheads'' for a range of modern missiles ''from nuclear technology that it developed itself.''
China, several officials said, simply went down the same path as other nuclear powers, helped along by the general knowledge of what the United States had achieved: proof that hydrogen bombs can be made very small but nonetheless very powerful.
''Every state has come to it,'' said one Federal official, referring to breakthroughs in atomic triggers by the Soviet Union, Britain and France. ''Now they've got it too.''
Mr. Hawkins, the head of international security studies at Los Alamos, which is clearly on the defensive because of the spy scandal, said the basic physics of bombs and missiles push weapons designers in roughly the same direction. To obtain the best performance, he said, engineers are invariably led toward narrow nose cones about 16 degrees wide -- if cut from a pie, a very modest slice.
''Once you realize that,'' Mr. Hawkins said, ''it drives every nation down similar paths. Eventually, all weapons systems will look alike. It has to do more with physics than espionage.''
That view is not universally accepted.
Dr. Henson, the analyst who first sounded the alarm at Los Alamos, said there was nothing in the design of missile nose cones that propelled a scientist to shape the core of an atomic trigger into an oval.
Do scientific and technical analyses automatically ''draw you to a watermelon?'' he asked, alluding to the shape of the top-secret design. ''That's not true.''
''It's beyond a shadow of a doubt,'' Dr. Henson added. ''Major espionage took place.''
American intelligence agencies are less categorical. Analysts have concluded that espionage played a role in Beijing's advance, but cannot identify a hard link comparable to the Soviet Union's theft in the 1940's of the American design for the first atom bomb.
''Everybody has come to the same conclusion,'' said a top Administration official who has closely scrutinized the secret data. ''We don't have a smoking gun.''
A Federal intelligence study done last year, which the Cox committee drew on, said American secrets lost between 1984 and 1988 let the Chinese ''accelerate their nuclear weapons program well beyond indigenous capabilities,'' a view that echoed the original Los Alamos finding.
A damage assessment by the American intelligence community, made public in April, said a mix of espionage, openly available data and scientific acumen had greatly lengthened Chinese strides. Stolen secrets, it said, ''could help'' Beijing develop a mobile missile and ''probably accelerated its program to develop future nuclear weapons.''
In June, the President's Foreign Intelligence Advisory Board, which did its own investigation, said both Congressional and Administration leaders had engaged in ''simplification and hyperbole'' in the spy case. Neither dramatic damage assessments nor categorical reassurances, it said, were wholly substantiated.
And Mr. Hawkins, the Los Alamos official, said the specific secrets known to have been seized by the Chinese, principally those detailed in the 1995 document, would have been little help to a bomb maker, and far from Mr. Trulock's road map. As for an H-bomb's innards, what designers call the physics package, Mr. Hawkins said the documents ''describe nothing significant.''
Mr. Cox insisted that highly classified intelligence data available to his committee showed a more persuasive case than has emerged publicly. ''There are more interpolating facts'' that closely tie lost W-88 secrets to Beijing's advance, he said.
But a Federal official cited intelligence data about China's atomic trigger showing it to be anything but an exact copy.
''It turns out the W-88's is slightly smaller,'' said the official, who believes Beijing may have made the advance on its own.
It remains unresolved how China got the W-88 secrets in the first place, but a consensus is emerging that the search for the leak narrowed too quickly to Los Alamos.
Studies by the Senate as well as the President's foreign intelligence board this year raised serious questions about whether the F.B.I. and Energy Department had too quickly focused on the weapons lab. No evidence has pinpointed it as the leak's source.
Mr. Vrooman, the head of counterintelligence at the laboratory from 1987 until 1998, noted that one secret document describing the design of the W-88 warhead went to 548 mailing addresses throughout the Government and military. Some Administration experts believe the data described by the Chinese in the 1995 document came from engineering plans or from secret manuals on military bases.
''That kind of information was widely available,'' said Dr. Drell of Stanford, who served on the President's advisory board investigation. ''The manuals that went out had pictures and numbers. If a submarine came in, and there was a problem, they had to know what they were dealing with.''
However Beijing made its miniaturization advance -- on its own, by theft or a combination of the two -- it is apparently proud enough to boast about it publicly, at least among its friends in the mountains of New Mexico. Dr. Henson said a Chinese arms scientist, Sun Cheng Wei, bragged of the breakthrough at Los Alamos a few years ago, telling an open seminar that China had forged significantly ahead in nuclear arms.
''What he said,'' recalled Dr. Henson, who attended the talk, ''was that for a long time they were dealing only with round designs, and then only watermelons.''
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