What was going on when I was born?

The Senate Finance Committee agreed today to repeal tax withholding on interest and dividends, but voted to attach to the repeal bill a package of unrelated measures, including President Reagan's Caribbean Basin Initiative and a trade reciprocity bill. Senator Russell B. Long of Louisiana, the ranking Democrat on the committee, charged that today's action would so clutter the repeal bill passed by the House earlier this month that the Democrat-controlled House would not accept it, even if the Republican-dominated Senate passed the measure with all the elements proposed today. Senator Long said that the committee's action would in effect derail the effort to repeal withholding. He added, however, that he would work instead to have the Senate endorse the repeal bill passed earlier this month by the House, without amendments. That bill would repeal the existing law that requires financial institutions to withhold 10 percent of their customers' interest and dividend payments, starting July 1.

The United States has asked Cuba to take back as many as several thousand of the 125,000 Cubans who came to this country as part of the boatlift from the port of Mariel in 1980, the State Department said today. The department, in a formal statement, said that Thomas O. Enders, Assistant Secretary of State for Inter-American Affairs, met on Tuesday with Ramon Sanchez-Parodi, the head of the Cuban Interests Section here, to make the request and officially inform him that until Cuba agreed to the return of the so-called ineligibles, no more immigrant visas would be granted to Cubans except for immediate relatives of those already in the United States. A department official said Mr. Enders gave Mr. Sanchez-Parodi a list of 789 people now in Federal prison in Atlanta who are subject to deportation under the legal status of ''final order of exclusion.'' The United States, the official said, wants these 789 to be accepted as part of a total that could run to ''a few thousand,'' he said.

Even before the discussions begin at the seven-nation economic summit conference this weekend, President Reagan has given the gathering his personal stamp, taking on an unusually ambitious role as host, chairman, moderator, note-taker and reporter on the proceedings. Already, his aides disclose, his preparations for the meeting in Williamsburg, Va., have drawn him into extensive personal correspondence with the other leaders and prompted him to take six months of tutoring on international economic affairs. The role Mr. Reagan has chosen marks a striking shift for a President whose hallmark has been delegating responsibility to his staff and Cabinet, letting them work out details and negotiate compromises on his behalf, especially in the field of foreign affairs. 'Dear Maggie,' 'Dear Francois' Mr. Reagan, bypassing the corps of diplomats and economic specialists that normally prepare the annual gatherings, has used four rounds of personal correspondence with the leaders of Britain, Canada, France, West Germany, Italy, Japan and the European Common Market to work out the arrangements and themes for their discussions in Colonial Williamsburg, according to White House officials.

The rebuilding of highways and bridges in the New York area is being stepped up this year, bringing mixed news for the motorist this Memorial Day weekend. In the long run, the roads will be smoother and safer. But for now, there will be more jackhammers, asphalt trucks, detours, orange traffic cones and ''People Working'' signs on local roads than at any time in nearly 25 years. Confronting these highway conditions will be an onslaught of motorists filled with the hope that Memorial Day will break a pattern of rainy and overcast weekends. Chances of that, however, are not good, according to the National Weather Service, which admits predictions of more than a day ahead are risky. The outlook, the service ventured, is for clouds, rain and below-average temperatures.

Governor Cuomo yesterday proposed using state employees and several hundred utility workers in the evacuation plans for the two Indian Point nuclear reactors. The Governor offered the proposal in an effort to satisfy Federal concerns about emergency procedures there. The workers would substitute for Rockland County firefighters, police officers, ambulance drivers, Health Department workers and high-ranking county officials. The Rockland County Legislature has ordered county workers to boycott emergency drills while the county develops its own emergency plan.

The International Monetary Fund has decided to postpone for at least a month the distribution of some $411 million in loans to Brazil because of doubts that the country is complying with an economic austerity program required by the I.M.F., monetary sources reported yesterday. The funds, part of $2.5 billion in loans promised by the I.M.F. for this year, were to become available to Brazil on June 1. Monetary officials said, however, that a delay in the loans would not have any serious effects on Brazil's already beleaguered economy. One of the austerity measures in its agreement with the I.M.F. required Brazil to reduce inflation to an annual rate of 85 to 90 percent, but it has shot up to an annual rate of 150 percent, from 99.7 percent last year.

International A return of several thousand Cubans who came to the United States as part of the boatlift of 125,000 Cubans that began in 1980 is sought by the Reagan Administration, the State Department announced. It said that Havana had been officially informed that until Cuba agreed to accept the ''ineligibles,'' no more immigrant visas would be granted to Cubans except for immediate relatives of those already in the United States. (Page A1, Col.1.) A top U.S. officer was slain in San Salvador. The American military attache said that Navy Commander Albert A. Schaufelberger, the deputy commander of the advisory group training Salvadoran troops, had been fatally shot outside the University of Central America by gunmen from a passing car. The commander was also head of the American military mission's security section. (A1:3-4.)

The Senate today gave final approval to a resolution endorsing President Reagan's plan to base 100 MX missiles in existing shelters and releasing $625 million for development of the huge new weapon. The 59-to-39 vote completed a sharp turnaround by Congress, which froze the money last December and directed Senate roll-call, page A18. the President to come up with a new basing plan for the missile. Today's decision also appeared to end a 10-year search for a home for the weapon, the largest designed by the United States. The critical factor in this changed attitude was a report by a Presidential commission last month that packaged the MX plan with two other proposals. One was that the Administration would also develop a smaller and more mobile missile for deployment in the 1990's; the other was that Mr. Reagan would be more flexible in arms control talks with the Soviet Union.

A late rally enabled stock prices yesterday to score their third consecutive advance in one of the heaviest trading sessions this year. The Dow Jones industrial average, which was off 1.26 points at 3 P.M., closed ahead 9.97 points, at 1,229.01. That was within striking distance of its record close of 1,232.59 on May 6.

When the leaders of the seven most powerful industrial democracies gather in the Capitol Building in Colonial Williamsburg this weekend, they will be meeting not far from Yorktown, Va., where George Washington - with powerful assistance from the French - won his decisive victory in the Revolution. The French-American alliance has endured ever since, punctuated periodically by differences over such things as Vietnam, the North Atlantic Treaty Organization and France's insistence in the 1960's to convert the dollars they held into gold. And next weekend a smoldering antagonism that has developed between President Reagan and President Francois Mitterrand might flare into open conflict. At the top of the agenda will be the serious misalignment and instability among the major trading currencies, an issue on which Paris and Washington are far apart. Then, too, there are frictions over high real interest rates in the United States and the simmering crisis over actual and potential defaults on billions of dollars of debt owed by developing nations.

Oil companies bid a record $3.47 billion for exploration rights on 656 Federal tracts in the Gulf of Mexico. The previous record, $2.7 billion, was set in 1980 on 147 tracts. The response by industry to the offering was hailed by Interior Secretary James G. Watt. (Page D1.) The Senate Finance Committee voted to attach a package of unrelated measures to a bill repealing tax withholding on income from dividends and interest. The rider included President Reagan's Caribbean Basin Initiative as well as a trade reciprocity bill. Advocates of repeal declared that the package, put together by opponents, would so clutter the measure as to threaten its passage. (D1.)

A COUPLE and a bachelor, looking for more living space in Manhattan, found similar solutions to the same problem. They bought brownstones, renovated them and created simple, large and airy living spaces. The renovations in both instances included complete gutting of the interiors, so the owners' triumphs were expensive ones. ''In an old house you're not sure what is really going on until you look under the surface,'' the bachelor, who is a doctor, said. Before their move, the couple found themselves in a situation shared by other well-to-do Manhattan families. They had lived in a rental apartment for 17 years, they had a growing child, they needed more room and they were at a stage in their lives when they could afford to look for their ideal cooperative apartment. But it was a time when prices for penthouses with views in prewar buildings were at their highest. ''One day,'' Diane Spigelman recalled, ''we just thought, 'Perhaps a house would be more sensible.' We could have a garden, and a house offers a certain kind of permanence and stability.''