WASHINGTON — John G. Roberts pairs a youthful demeanor with a sharp, seasoned legal mind that has impressed Ivy League professors, government lawyers and U.S. presidents.

Befitting his age of 50 and limited time on the appellate court, the book on his judicial decisions remains a work in progress.

President Bush on Tuesday tapped Roberts to become the nation's 109th Supreme Court justice, introducing the Harvard honors graduate, former clerk to William Rehnquist and successful Washington attorney to the nation in prime time.

"He has argued 39 cases before the Supreme Court and earned a reputation as one of the best legal minds of his generation," said the president as Roberts stood at his side, broad shoulders hinting at his days as captain of his high school football team.

Roberts, often cited by friends for his self-deprecating wit, recalled his appearances before the high court.

"I always got a lump in my throat whenever I walked up those marble steps to argue a case before the court, and I don't think it was just from the nerves," he said.

There were wins — and losses, including one rout.

"One case he lost 9-0 and he had to call up his client, which is never a fun thing to do," recounted Richard Lazarus, a Georgetown University law professor who has known Roberts for nearly three decades and roomed with him in Washington. "His client was just incredulous, beside himself. 'How could we have lost 9-0?' John finally just quipped back, 'Because there are only nine justices.'

"That's very typical. Fast and funny and sometimes self-deprecating," Lazarus said.

Roberts was born in Buffalo, N.Y., and grew up in Indiana when his family moved after second grade. He worked in the steel mills to pay for Harvard, where he majored in history and graduated summa cum laude.

William P. LaPiana, now a professor at New York Law School, recalled Roberts' joking about the effect of a top grade he received in a course on American intellectual history.

"I remember him walking into the room and saying, 'Gee, maybe I can get my head through the door,"' LaPiana said.

A prelaw adviser to Roberts at Harvard, LaPiana said, "Post-adolescents who are really bright sometimes get carried away with themselves, and he certainly never did."

Roberts excelled at Harvard Law School, a magna cum laude graduate in the class of 1979. He embarked on a Washington attorney's career with a clear upward trajectory — clerking for an appeals court justice, then Rehnquist, joining the Reagan Justice Department.

A change in administrations led to a lucrative private practice at the venerable Hogan & Hartson LLP. Roberts earned a salary of $1,044,399 from the firm before resigning as a partner in May 2003, according to a financial disclosure report he filed this year.

Roberts reported a long list of stock holdings, including investments in drug companies and tech firms. He also reported a one-eighth interest in a cottage in Knocklong, Limerick, Ireland, which he valued at $15,000 or less.

He reported that his wife drew a salary from Pillsbury Winthrop Shaw Pittman, but he didn't disclose the amount. Jane Sullivan Roberts, a graduate of Georgetown University Law Center, is a partner in the firm specializing in transactions involving technology.

The couple have two adopted children, Jack and Josie, both under 6. Jack Roberts, in short pants and saddle shoes, took advantage of the White House stage Tuesday night, dancing during the president's announcement.

Roberts is a relatively young nominee for the Supreme Court, where eight of the nine justices are over 65.

"He is not only absolutely brilliant, but he has good common sense and good sense about people. I do not think the Democrats will be able to touch him," said Patrick J. Schiltz, a professor at the University of St. Thomas School of Law and a friend of Roberts. "He is incredibly charming, he has movie-star looks. ... He has been an Eagle Scout in his personal life."

Still, getting to the federal bench took some time.

The first President Bush selected Roberts for the federal court of appeals, but he never was given a hearing by the Democratic-controlled Senate. The current President Bush tapped him for a second time in 2001, but that nomination died, too.

Bush nominated him again in January 2003 and the Senate ultimately confirmed him in 2003 on a voice vote without serious opposition.

Roberts' nomination to the appellate bench attracted support from both ends of the ideological spectrum. Some 146 members of the D.C. Bar, including officials from the Clinton administration, signed a letter urging his confirmation.

The letter stated: "He is one of the very best and most highly respected appellate lawyers in the nation, with a deserved reputation as a brilliant writer and oral advocate. He is also a wonderful professional colleague both because of his enormous skills and because of his unquestioned integrity and fair-mindedness.

Roberts is well-known in Washington circles and a favorite of the conservative lawyers of the Federalist Society. He tries to avoid labeling his judicial approach, however, saying at his confirmation hearing, "I don't necessarily think that it's the best approach to have an all-encompassing philosophy."