What was going on when I was born?

International One of the biggest protests in Warsaw since martial law was imposed 17 months ago occurred as about 20,000 Poles attended the funeral and marched for nearly two hours to the burial of a 19-year-old youth who died after being detained by the police. The signature of the outlawed union Solidarity was fastened to the front of the coffin. (Page A1, Columns 2-3.) Rifts among Western leaders may mark the economic summit conference in Williamsburg, Va., on May 28-30, Reagan Administration aides fear. They have sought to assure a harmonious meeting, but there are major differences between Washington and Europe, including France's charge that American budget deficits and high interest rates are damaging the world economy. (A1:4.)

The stock market registered a broad loss yesterday in less active trading as the Dow Jones industrial average fell 12.19 points, to 1,191.37. It was the first time the closely watched barometer has closed below the 1,200 level since April 25, when it closed at 1,187.21. William M. LeFevre, vice president of investment strategy at Purcell, Graham & Company, attributed the selloff to disappointment over the rate of increase in the gross national product in the first quarter and the day's sharp drop in bond prices. The Commerce Department reported early in the session that the gross national product rose at a seasonally adjusted annual rate of 2.5 percent in the first quarter, lower than expected.

The economy grew at a 2.5 percent annual rate, after adjustment for inflation, in the first quarter this year, slower than originally estimated, the Commerce Department reported today. The downward revision from an original estimate of 3.1 percent was a result of a sharper decline in inventories than had been assumed, however, and does not change the outlook for significantly stronger growth this quarter, economists said. Several measures of corporate profits released today left a mixed picture of business activity in the quarter. The Commerce Department's preferred measure, profits from current production, jumped 12.4 percent from last year's fourth quarter, after having slipped 1 percent in the fourth quarter. The better-known measure of after-tax profits declined 4.6 percent after falling 1.3 percent in the fourth quarter.

Time Inc. announced yesterday that it would spin off its large forest products business to concentrate on publishing and video operations. The forest products group accounted for $1.1 billion in revenues last year, or 32 percent of Time Inc.'s consolidated revenues of $3.6 billion. The group will now be incorporated as a separate company whose shareholders will be Time Inc. shareholders. Following the spinoff, Time Inc.'s principal lines of business will be the publishing of magazines and books, and video, which includes Home Box Office, the nation's largest cable service, with more than 12 million subscribers, and the American Television and Communications Corporation, the largest cable system.

The dance company of the innovative choreographer Twyla Tharp will make its only appearance in the New York area this season at 8:30 tonight in the C.W. Post Concert Theater in Greenvale, L.I. On the program are ''Sue's Leg,'' danced to the music of Fats Waller; ''The Fugue,'' which has no music (footsteps create polyphony); ''Short Stories II'' and ''Assorted Quartets.'' Tickets are $12.50 and $15. The campus is about an hour from Midtown Manhattan. Directions and reservations: (516) 922-0061. A MIME OF MASKS Daniel Stein, an American mime based in Paris, who has received impressive reviews, does not wear white-face. But in his latest work he does wear unusual masks, such as a door, a slide rule and, believe it or not, a 13-member chorus. The work, receiving its world premiere at the Dance Theater Workshop, 219 West 19th Street, tonight at 11, is called ''Inclined to Agree.'' It explores the nature of truth - symbolized by a curtain of plumb lines - and peoples' slanted points of view - manifest in tilted chairs and other objects. Mr. Stein says he's a ''concert move-ician,'' explaining that he ''plays'' movement, just as a musician plays music. Tickets: $6. Reservations recommended: 924-0077.

Garbed in a tan army-style helmet, khaki work suit and white safety spats, Yukio Okada strides among the workers - a front-line warrior in New York City's multibillion-dollar effort to refurbish its subway system. The resonant clang of metal against metal assaults the ears. The vista in the cavernous factory is punctuated by the white-light flashes from welders' torches. The smell of freshly cut steel is heavy in the air.

The economy grew at a 2.5 percent annual rate in the first quarter, more slowly than forecast, the Commerce Department said. But the shortfall resulted from a sharper-than-expected decline in inventories, economists said, so it does not change the outlook for stronger second-quarter growth. Also, first-period corporate profits soared 12.6 percent, the biggest such gain in five years. (Page D1.) The Senate rejected a budget plan seeking the minor tax increases that President Reagan and the G.O.P. leadership favor. A similar plan was defeated a week ago. (A1.)

The Senate voted 50 to 49 late tonight to adopt a 1984 budget with tax increases opposed by President Reagan as too large. Senator Pete V. Domenici, the New Mexico Republican who is chairman of the Budget Committee, changed his vote to yes at the last minute, providing the winning margin. The Senate's action set the stage for a conference with the Democratic-controlled House of Representatives, possibly next week, a session that is expected to be long and difficult. It ended months of efforts by the majority leader, Howard H. Baker Jr. of Tennessee, to lead the 54 Senate Republicans to a plan that Mr. Reagan would support. Reagan Has Threatened Veto The President said at a news conference Tuesday: ''I will not support a budget resolution that raises taxes while we're coming out of a recession. I will veto any tax bill that would do this.''

Leon Degrelle is living very well these days and at first glance one might take him for a retired businessman, one of the thousands who come down from northern Europe for the easy life in the Spanish sun. He has a comfortable villa tucked away in Torreblanca on the Costa del Sol and an apartment in Madrid with a gardened terrace that overlooks an elegant boulevard. It is decorated with Roman antiquities from southern Spain - vases, sculptures, chariot decorations and tear vials - displayed in glass cases. ''Above all, I live for beauty,'' he said in an interview in a cultivated, slightly world-weary tone. Mr. Degrelle no longer needs his Spanish identification card in the name of Leon Jose de Ramirez Reina, but he keeps it as a souvenir. Seventy-seven years old next month, he has combed-back, receding hair and a spreading paunch so that he can no longer fit into his SS uniform, which is kept in a closet.

About 20,000 Poles went to the funeral today of a young man who died after being in police custody. It was one of the largest demonstrations in the capital since martial law was imposed 17 months ago. The once-familiar red signature of Solidarity, the outlawed independent union, was fastened proudly to the front of the coffin of 19-year-old Grzegorz Przemyk. As the sprawling procession trudged for nearly two hours to the cemetery the mourners held up the V-sign that has become the symbol of resistance to the authorities.

The Canadian Government has introduced legislation to set up a clandestine intelligence service with broad authority to intercept mail, install recording devices and surreptitiously break into homes or offices. The legislation, which is raising concerns among civil liberties activists, also provides penalties of five years' imprisonment for anyone revealing information from which the identity of a covert operative or informant ''can reasonably be inferred.'' Panel Recommended Move The bill setting up the Canadian Security Intelligence Service was introduced in Parliament Wednesday, almost two years after a blueribbon panel recommended that the Royal Canadian Mounted Police surrender responsibility for national security to a civilian agency. The commission made its recommendation after finding that Mounties had committed crimes such as arson, forgery and breaking and entering in what some of their officers asserted were matters of national security. Though criminal charges were filed against some of the police, none have gone to jail and only one has been convicted.

A Federal judge has denied New York City's bid to raise the population limit for its jails on Rikers Island. Three months ago, city officials told the judge, Morris E. Lasker of Federal District Court in Manhattan, that unless some relief were granted, they might have to release some inmates to accommodate newly arrested people. Since then, the jail population has dropped, and yesterday city officials said the problem had abated somewhat. Mayor Koch, in a statement, said: ''Judge Lasker's decision has no immediate impact on our system. We will not be releasing any of the 10,027 inmates now in our system.''