What was going on when I was born?

The committee of American Roman Catholic bishops preparing a pastoral letter on nuclear arms has reversed itself and will suggest language to intensify the letter's opposition to such weapons, according to a committee staff member. The five members of the committee have decided that the letter should call for a ''halt'' to the ''testing, production and deployment'' of new nuclear weapons, said the Rev. Brian Hehir, the staff member of the United States Catholic Conference who is attached to the committee. In a meeting beginning Monday in Chicago, the country's 284 Catholic bishops will debate the 44,000-word pastoral letter, a document that has placed the bishops in the forefront of the wideranging discussion about the morality of nuclear arms. They are expected to approve a final version of the letter at their two-day meeting.

The explanations offered by the Argentine military for the disappearance of thousands during its campaign against leftist terrorists in the 1970's were roundly rejected today by many Argentines. A wide range of political and labor leaders as well as church officials, intellectuals and major human rights groups said in separate statements that the military's television broadcast to the nation Thursday failed to give details of what happened to the people, estimated at more than 6,000, who had disappeared or to say how many were dead. Most of the officials acknowledged the gravity of the leftist threat in the mid-1970's, but many accused the military of having used ''state terrorism'' to counteract the threat. Despite widespread expectations after the broadcast, the Government did not give details today on the fate of any of the missing people. About 20 families, in response to the broadcast, went to the Interior Ministry this morning to look at a list the Government promised to provide of those who are missing. They were told to come back later.

The Reagan Administration is trying to head off a ban on covert American aid to Nicaraguan rebels by seeking changes in a bill before the House intelligence committee, according to Administration officials. These officials said Deputy Secretary of State Kenneth W. Dam was in touch with Representative Edward P. Boland, the committee chairman. Mr. Boland is the principal author of a bill to ban all covert aid through the Central Intelligence Agency to groups operating ''in and against'' Nicaragua. The committee is to vote on the measure next week. Committee members met at the White House with President Reagan on Tuesday. After the meeting Mr. Boland, a Massachusetts Democrat, and Clement J. Zablocki, a Wisconsin Democrat and chairman of the House Foreign Affairs Committee, formally submitted the legislative ban. But they coupled it with a proposal for $80 million in aid to Central American nations to help them halt the flow of arms and munitions from Nicaragua to insurgents in neighboring countries.

The Board of Education waited an extra day to choose Anthony J. Alvarado as Schools Chancellor because city lawyers thought they might have new grounds to reinstate the Board of Education's first choice, Deputy Mayor Robert F. Wagner Jr. The board was told Wednesday that it might have grounds to circumvent the Education Commissioner's rejection of Mr. Wagner. But the next day, according to participants, it received contrary advice and chose Mr. Alvarado. In any case, Mr. Wagner said yesterday that he had decided Thursday morning that it would be unwise and potentially damaging to begin a legal challenge, even if he could win it.

Harold Washington was sworn in today as the city's 42d Mayor in an unusual and emotional inauguration ceremony. In his remarks, the new Mayor described the city's financial problems as ''enormous'' and said he would order sweeping cutbacks and layoffs in the government, beginning on Monday. Higher Deficits Reported Flanked on the flower-draped stage at Navy Pier by former Mayor Jane M. Byrne and dozens of state and national officials, the 61-year-old Mr. Washington, the first black to lead the city, stunned many people when he said the city's finances were in much worse shape than Mrs. Byrne had acknowledged. But the estimated 3,200 people watching the ceremony cheered the new Mayor as he recited the city's budget troubles and his plans to relieve them. ''Our school system,'' he said, ''is not $100 million short next year as we believed during the mayoral campaign, for we now find that the income may be $200 million less than the expenditures of that vast bureauracy.

The Government's index of leading economic indicators rose 1.5 percent in March, the Commerce Department reported today, a signal that the economic recovery, which began in the first quarter, will continue to move ahead. The rise in the index was spurred by jumps in three of its components: the stock market, the money supply and the average workweek. It was the seventh consecutive monthly gain in an index that is intended to forecast economic trends. The index rose 1.4 percent in February and 3.2 percent in January.

Those who disparage David Thebehali, the canny and affable ''Mayor'' of South Africa's largest black settlement, like to point out that he gained his position with only 97 votes in a widely boycotted election five years ago. Disputing that tally with a wounded expression, Mr. Thebehali insists he was actually the choice of 295 of Soweto's inhabitants - none of whom, including himself, have an unambiguous claim to citizenship under the country's laws. Since Soweto has a population of at least 1.2 million, Mr. Thebehali's mandate can hardly be regarded as overwhelming, even by his own generous estimate. But it was a start, and he has been building on it ever since, using the limited powers conferred on him as the indirectly elected chairman of the Soweto Community Council to do favors for potential voters. Since 1978, he says, he has met personally with 78,000 Soweto inhabitants to help them out of snags with the white bureaucracy, ease their housing problems or even counsel them on their marriages.

Premier Rene Levesque said today that his party would have to stoke up what he described as a ''dormant'' separatist consciousness in Quebec to pave the way for an election within two years that will clearly be run on the issue of independence. In a two-hour interview in Hull, just across the river from Ottawa, Mr. Levesque said his Parti Quebecois, aware of its low rating in public opinion polls, was gearing up for a campaign he hopes will result in a mandate to proclaim independence. ''Our position is that if we get anything that looks like 50 percent of the vote, which automatically would mean that we won 60 percent of the French-speaking vote, that's a mandate,'' he said. ''If we get it we go ahead by all legitimate means.''

Prime Minister Menachem Begin discussed with Secretary of State George P. Shultz today a possible compromise on the role of Maj. Saad Haddad, the southern Lebanese militia commander, Israeli and American officials said. Major Haddad's future has been one of the chief unresolved issues in the negotiations on an Israeli troop withdrawal from Lebanon. The officials said Mr. Shultz informed Mr. Begin that President Amin Gemayel and other Lebanese officials had told him on Thursday in Beirut that they would consider allowing Major Haddad to remain in southern Lebanon in a lesser role than that of overall commander of the forces that will be in control of the border region. A senior aide to the Israeli Prime Minister said that in the meeting with Mr. Begin, Foreign Minister Yitzhak Shamir and Defense Minister Moshe Arens, Mr. Shultz was given an Israeli response that is ''a kind of compromise, a shift on a limited point.'' He said that when the Secretary of State returns from transmitting this to the Lebanese on Saturday ''we might be able to find an agreed solution.''

Banks, railway stations and public buildings here and in three other French cities were damaged today by a series of bombs. The Corsican National Liberation Front, a Corsican separatist group that was banned by President Francois Mitterrand in January, claimed responsibility for the 15 explosions, which caused no injuries.

An interagency working group is considering revisions of the Administration's strategic arms proposal that could narrow differences with the Soviet position and lead to the development of a new single-warhead missile, Administration officials said today. The United States originally proposed restricting each side to 850 intercontinental missiles on land and sea. Two officials said the working group was considering raising or abandoning the limit. A White House official said the discussions so far had been strictly at the working level of the State Department, Pentagon, the Arms Control and Disarmament Agency, Central Intelligence Agency and the National Security Council staff.

The head of the Turkish military junta said today that a general election would be held Nov. 6. Gen. Kenan Evren, in a speech at a military exercise at Erzincan, said those who intended to form political parties should unite into bigger parties to create a stable majority in the Parliament and give the country stability for the next five years. A ban by the junta on political activity was partly lifted last Sunday with a decree that allowed citizens to begin to form political parties. Political activity was banned when the military took over in September 1980, and all political parties were abolished in 1981. Determined not to tolerate re-creation of the defunct parties, the junta reserved the power to veto any founding members of the new parties who were leaders of the old ones.