QAIN, Iran, May 11— Iranian officials appealed for help, volunteers hurried to deliver aid, and survivors dug out and washed the dead for burial today after a major earthquake devastated northeastern Iran, killing 2,400 people, according to estimates. That toll was expected to rise.

More than 155 aftershocks, some as strong as 5.5 in magnitude, shook what little remained standing today, forcing many of the 40,000 people left homeless in this remote mountain region to camp outdoors amid the rubble of scores of stricken villages.

Iranian military aircraft flew in food, clothes and medicine, and thousands of volunteers arrived in convoys of trucks and buses to dig through the mounds of brick and cement, often with bare hands, in the search for the living and the dead.

In most villages of Khurasan Province, which abuts Iran's rugged frontier with Afghanistan, streets had been transformed into streams of rubble. Some survivors beat their chests and wailed. Others gathered up the bodies and buried them in mass graves.

Officials estimated that at least 6,000 people were injured in the quake, which registered 7.1 on the Richter scale and struck at midday on Saturday. It was Iran's third severe quake this year, and it hit just 10 weeks after a major quake in northwestern Iran killed nearly 1,000 people in February.

Most of the damage in the latest disaster centered on a 60-mile patch of land between the towns of Birjand and Qain, a region speckled with saffron fields and the simple mud huts of poor farm villages.

In one of those villages, 110 young girls were killed nearly at once, as their elementary school collapsed and buried them under jagged slabs of steel and concrete. At least 2,000 people died in the dozens of villages in the area around Qain, 394 in Birjand, and two in the town of Khavaf, the official Islamic News Agency said.

It also reported heavy damage across the border in Afghanistan, a country already ruined by many years of civil war and crowded with refugees.

In Kabul, the Afghan capital, international aid workers said that so far, only five people had been reported killed, but that relief teams were still en route to the remote western region to assess the full extent of the damage.

Iranian officials estimated the damage in their own country at $67 million and appealed for international assistance. From Tokyo, the United Nations Secretary General, Kofi Annan, urged countries ''to respond promptly and with generosity.''

France dispatched a cargo plane loaded with 39 tons of blankets, tents, clothes and food. Switzerland sent a rescue team and trained dogs to help search for survivors, although Iran turned down an offer of a larger contingent.

$(A British group, International Rescue Corps, which specializes in locating and rescuing people trapped under debris, was refused visas by the Iranian Embassy in London, Agence France-Presse reported. It said the group had planned to send a team of 15 people, but was told that enough rescue crews had already arrived at the disaster site.$)

Many other countries, particularly those from the surrounding Persian Gulf region, sent messages of condolence to the families of the victims and the Iranian Government.

In Washington, Mary Ellen Glynn, a spokeswoman for President Clinton, said the United States would send aid, if requested, through a third party, like the International Committee of the Red Cross and Red Crescent. ''If it's necessary, we would certainly contribute,'' she said.

''I believe that despite our differences with Iran -- which are considerable and very, very strong -- this will be viewed as a humanitarian issue,'' Bill Richardson, the chief American delegate to the United Nations, said on CNN.

The Iranian Red Crescent sent 9,000 tents, more than 18,000 blankets, and canned food, rice and dates. The Iranian Government delivered at least 80 tons of aid to the region aboard four American-made C-130 cargo planes and six helicopters, presumably to the provincial capital of Meshed, a city of two million where much of the relief effort was being coordinated.

From there, the relief supplies must still be trucked for five hours over rough terrain and along narrow, unpaved roads to the affected villages, many of them miles from the nearest hospital.

Temperatures in the mountain region here dropped to 41 degrees overnight, and then rose to 84 during the day, raising concern among officials and villagers that the many bodies still buried under the rubble might begin to rot and spread disease.

''Much needs to be done,'' said Reza Alavi, a civil servant leading relief efforts in one of the villages. ''The priority is to remove the dead bodies and bury them as soon as possible.''

Makeshift hospitals were filled with those wounded, many wrapped in blood-soaked bandages or with cuts and broken bones. Sacks of intravenous blood supplies were suspended from donated coat hangers.

''I can't deal with this alone,'' Dr. Mohammad Hossein Mozaffar said, as he put a cast on the leg of a crying 5-year-old boy in Qain.

Most of the villagers in the region are subsistence farmers who either tend camels or sheep or grow wheat and saffron. Many of the injured appeared as if they were weak and malnourished even before the quake had struck.

Tens of thousands of villagers camped out in the streets today, fearing the trembling of the quake's many aftershocks, some strong enough to cause considerable damage of their own.

Nearly all of Iran is in an area prone to earthquakes. The country is frequently shaken by them, but few as powerful as the one that struck on Saturday, the third severe quake of the year.

In early February, about 80 people were killed in Bojnurd, in the north of Khurasan Province near the border with Turkmenistan, when quakes measuring 6.1 and 5.4 rocked the region.

Later that month, on Feb. 28, a major quake destroyed much of the area around the northwestern city of Ardebil, near the border with Azerbaijan. That quake, which measured 6.1, killed 965 people and left 40,000 people homeless, officials estimated.

This latest quake, though, was the strongest to strike Iran since June 21, 1990, when quakes of 7.3 and 7.7 in magnitude destroyed the northwestern provinces of Gilan and Zanjan, near the Caspian Sea. Those quakes, among the worst to strike anywhere this century, killed from 35,000 to 40,000 people and left half a million people without shelter.

In this latest catastrophe, one of the worst-hit villages was tiny Abiz, 55 miles east of Qain, where about a third of its residents died when the quake hit on Saturday.

Today, anguished villagers searched the ruins of homes for survivors, and heard a faint cry and pulled Alireza Rayee, 32, from the rubble that had threatened to entomb him.

One rescuer hurried to give him water, and another wiped the dirt from his face and fanned him with a piece of cardboard. Mr. Rayee's mother cradled her son's head in her lap and wept.

''God has given my son a second life,'' she said.

Photos: Iranians began sifting the rubble for victims and preparing bodies for burial yesterday, after an earthquake. A group of survivors in Ardakul used a blanket as a stretcher to carry the body of a victim. (Mohamad Sayyad/Canadian Press); A quake in Iran injured at least 6,000. Iranian television showed a man crying over an injured child yesterday at an emergency center in Qain. (Associated Press) (pg. A8) Map of Iran showing the location of Qain: Most of the damage caused by an earthquake in eastern Iran centered on a 60-mile patch between the towns of Qain and Birjand. (pg. A8)