What was going on when I was born?

The 11-day siege of the Libyan Embassy ended peacefully today as 30 diplomats and other occupants of the building in central London filed silently out, hands at their sides, eyes fixed straight ahead, and clambered into police vans. Scotland Yard took the Libyans to a ''safe house'' in the London suburbs, where they were closely questioned, before putting them aboard a Libyan Arab Airlines flight to Tripoli. The group was believed almost certainly to have included the gunman who, according to witnesses, killed a policewoman, Yvonne Fletcher, and wounded 10 opponents of Col. Muammar el-Qaddafi, the Libyan leader, who were demonstrating outside the embassy on April 17. Tonight, the Libyans were reported to have received a vociferous welcome in Tripoli, the Libyan capital. In a carefully synchronized move, the remaining British officials in Libya hauled down the Union Jack over their embassy, and all but two of them then left for home. (Page 3.)

Walter F. Mondale, bowing to criticism from his rivals for the Democratic Presidential nomination, announced today that he would return about $300,000 contributed to committees supporting delegates who back his candidacy. Mr. Mondale acted two days after announcing that he would terminate all such committees but would not return the money they had raised. On Thursday he had told reporters that it was all right for the groups to keep the money, which came largely from organized labor. Mr. Mondale said that, because of questions raised about the finances of the delegate committees, the money the groups had spent in behalf of the Mondale candidacy would be counted toward his $20.2 million Federal limit on spending in the nomination battle.

In the 26 years J. E. Adkinson has spent as a pipe welder at Ingalls Shipbuilding here, he has helped build anything from submarines and frigates to freighters and destroyers. But he says he has never worked on anything quite like the U.S.S. Iowa. ''This country has a ship it can be real proud of,'' says Mr. Adkinson, who is 44 years old and has spent the last several months helping refit the World War II battleship for sea duty. ''Working on her was like working with American history.''

More than two years after the long and dramatic trial in which Claus von B"ulow was convicted of twice trying to murder his wealthy wife, the Rhode Island Supreme Court overturned the jury's verdict today and ordered a new trial. A majority of the justices said the evidence justified conviction if considered in the light most favorable to the prosecution. But the court ruled some of the evidence had been tainted by lack of a search warrant and should not have been admitted. Furthermore, the court said evidence that might have been helpful to the defense had been improperly supressed by the trial judge. Reacting calmly to the decision, Mr. von B"ulow said in an interview in New York City that he would not necessarily object if prosecutors sought a new trial, although he said he was reluctant to subject himself to another such ordeal. ''I obviously want to be vindicated, and I feel that our new evidence would vindicate me completely at a new trial,'' he said. (Page 7.)

Victor M. Thompson Jr. resigned today from the board of the Synthetic Fuels Corporation, amid widening charges of improprieties. His departure leaves the embattled Government-sponsored company without a quorum to conduct business. At least two critics of the corporation on the Senate Energy Committee, Bill Bradley of New Jersey and Howard M. Metzenbaum of Ohio, both Democrats, quickly seized on the existence of a crippled board to try to force a review of the company's mission to spur development of synthetic fuels, or even to shut it down. The corporation, created under a law signed by President Carter with great fanfare in mid-1980, was designed to be the catalyst for private-sector development of a major new American industry. It was envisioned that the Government would provide up to $88 billion in aid but, largely because of the decline in world oil prices, interest in the development of synthetic fuels has waned.

Thousands of criminals sentenced to probation in New York City each year are going virtually unsupervised by the city's Department of Probation, state and local officials say. The department is so understaffed, they say, that many probationers are committing new crimes without fear of being caught and sent to prison. Unless the system is overhauled, said Lawrence T. Kurlander, Governor Cuomo's Director of Criminal Justice, ''probation has ceased to exist as a viable proposal in the city of New York.'' The Probation Department has been overwhelmed by a problem that plagues much of the city's criminal- justice system: The agency's work load expanded while its staff and budget were cut. On average, a probation officer in the city handles about 215 cases at once - more than double the state average.

President Reagan stressed to Chinese leaders Friday that China and the United States have parallel international interests, but he encountered complaints about his policies in several parts of the world and found that parts of a televised speech had been censored by the Chinese. This morning, the White House issued a formal statement of regret that some of Mr. Reagan's remarks - about the need for belief in God and in democracry, and a critical reference to the Soviet Union - had been deleted on Chinese television Friday night. (Page 4.) Prime Minister Zhao Ziyang met Mr. Reagan for two 90-minute sessions, one on Friday morning on international problems and another in the afternoon on United States-Chinese concerns. During the meetings, Mr. Zhao voiced complaints about the Reagan Administration's policies in Central America, the Middle East and Taiwan and about the deployment of new American missiles in Europe. Afterward, Hu Yaobang, General Secretary of the Chinese Communist Party, spent an hour talking with Mr. Reagan.

A Federal judge fined a Swedish electronics company $3.1 million today for illegally exporting strategic American material to the Soviet Union, an act he called ''treacherous conduct.'' The United States said export of the equipment enabled the Soviet Union to expand its military radar ability. The action was the largest criminal penalty ever imposed for violating United States controls on the export of strategic goods to the Soviet Union. The company, Datasaab Contracting A.B., based in Jarfalla, Sweden, bought parts for a sophisticated Soviet radar system in the United States and forwarded them to the Soviet Union in violation of the terms of an export license granted by the Commerce Department in November 1977.

Two years after he traveled to Chicago for the beginning of a lawsuit, the Mayor of this fishing village on France's northern Brittany coast says he feels enthusiastic about American justice. So do the 54 other mayors from this area who accompanied him; so, too, does the French Government. The Mayor, Alphonse Arzel, presides over a village where brightly painted boats bob up and down on an emerald sea and where beaches are silvery clean. The lawsuit had to do with the sharp change that occurred here six years ago after the supertanker Amoco Cadiz, its rudder broken, drifted onto rocks just beyond the harbor's entrance and spewed 70 million gallons of crude oil.

An Egyptian police sergeant has been charged with stealing weapons this month that were used in the assassination of President Anwar el-Sadat in 1981.

The Libyans being repatriated from London returned to a vociferous welcome here late tonight as the withdrawal of Libyan and British diplomatic personnel from their respective embassies was completed. The diplomats and others attached to the Libyan Embassy in London landed here just before midnight.

Defense Minister Moshe Arens was said today to have appointed a commission to investigate the deaths of the four Palestinians who hijacked an Israeli bus two weeks ago. The report came amid accumulating evidence that at least one of the hijackers was captured alive and killed later. There was no formal announcement of the panel's creation. An official here in a position to know said the members included experienced military and intelligence people. The official said the panel was to be headed by a former army general, Meir Zorea, who was on the commission that investigated Israel's unpreparedness for the 1973 war. He recently retired as Comptroller of the Defense Ministry.