What was going on when I was born?

Secretary of State Alexander M. Haig Jr. said today that the United States would play ''a more active role'' in coming weeks in trying to end the Iraqi-Iranian war. He seemed to warn Iran that if it spread the conflict into neighboring nations Washington would protect its ''vital interests'' in the Persian Gulf. In the Administration's first comprehensive Middle East policy statement, Mr. Haig discussed at length the Iraqi-Iranian war, the stalemated Egyptian-Israeli negotiations on Palestinian self-rule and the Lebanon crisis. In connection with the Egyptian-I@sraeli talks, Mr. Haig said there should be a ''redoubling of efforts.'' Administration officials said that the United States had raised the possibility of a three-way meeting involving President Reagan, President Hosni Mubarak and Prime Minister Menachem Begin next month but that nothing had been set.

An article about Brentano's Inc. in Business Day yesterday incorrectly reported the amount owed by the book chain to the Ingram Book Company. It is $277,000.

''My days of stay in Great Britain will still be an incessant prayer in favor of peace, raised together with all God's people, who carry sculptured in their hearts the words of Christ: 'Blessed are the peacemakers, because they will be called the sons of God.' '' - Pope John Paul, in letter to President Leopoldo Galtieri of Argentina. (A18:4.)

The Justice Department filed suit today to force the Tribune Company of Chicago to sell five Florida publications that it acquired in 1980, an antitrust challenge that seems likely to have wide repercussions in the newspaper industry. Acquisition of the five papers, all of them weeklies published and distributed in Osceola County near Orlando, was said by the Government to have lessened substantially or to have eliminated competition for local advertising, in violation of the Clayton Act barring anticompetitive mergers. The Sentinal Star Company, a Tribune Company subsidiary based in Orlando, which publishes the city's only daily newspaper, was also named as a defendant. The subsidiary bought the smaller papers for $4.14 million.

AS children are increasingly exposed to images of nuclear war on television and in print, parents, teachers and mental-health professionals are being confronted with the psychological effects of those images. Some typical fears of young people were expressed at a recent meeting of Future Generations, a new youth organization in New York that opposes the nuclear-arms buildup. Susan Markowitz, a 12-year-old student at the Bank Street School, was talking about the first time she became aware of the possibility of nuclear war. ''At the beginning of this year when the class started reading articles,'' she said, ''I got very frightened that the world could blow up.'' Rachel Dretzin, 16, who goes to the Dalton School, said she thought her schoolwork had been suffering lately and said she frequently had nightmares. ''Last week I dreamed that a bomb went off in my kitchen and there were bombs all over the house,'' she said. ''When I walk in the street, I look at things and imagine what would happen if they just disappeared.''

A sports article yesterday about Tracy Austin included an incorrect description of her match against Chris Evert at Wimbledon in 1977. Miss Austin won the first game but lost the match in straight sets, 6-1, 6-1.

As millions of motorists take to the highways for the Memorial Day weekend, they will find that gasoline prices are lower than they were a year ago -by about 15 cents a gallon - the first time in five years that this has happened. Supplies are plentiful and many service stations on major routes will be open around the clock. But gasoline prices are beginning to rise again. In the past six weeks, retailers have been raising prices in response to increases at the wholesale level. Since mid-May, service stations nationwide have increased the average price for all grades of gasoline by nearly 3 cents a gallon, to $1.21, according to Daniel Lundberg, an industry analyst.

''This is a town meeting, and this is my town,'' said Toni Fitzpatrick at a meeting in Murray Hill Tuesday night at the Community Church on 35th Street near Park Avenue. ''I want to make a statement that nuclear war is not unthinkable. We dream about it, we have nightmares about it.'' She was one of 4,000 New Yorkers who attended 11 neighborhood meetings in Manhattan that night to discuss a resolution to freeze ''the testing, production and deployment of nuclear weapons'' and to ''transfer funds from the military budget to human needs.''

America's foreign trade deficit narrowed to $322 million in April, the closest the nation has come to a balance in merchandise trade since a one-month surplus more than six years ago, the Government reported today. The improvement was not a result of any surge in United States competitiveness - exports by American companies actually declined a bit in April. But imported oil hit its lowest level in the nine years that the Government has been keeping track, and a wide range of other imports were also down substantially as the recession continued to hamper economic activity.

The Senate Foreign Relations Committee, strongly criticizing El Salvador's recent moves to alter or delay key land redistribution programs, called today for a $100 million reduction in military aid proposed for that country. In a vote of 12 to 0, the panel cut the Reagan Administration's military aid package to El Salvador for next year from a proposed $166.3 million to $66 million. Essentially, that is the same amount that El Salvador is receiving this year in military and economic support. In El Salvador, a spokesman for the Defense Ministry said the committee's vote was based on an ''incorrect'' interpretation of the measures taken by the Salvadoran Government, United Press International reported.

Congress vetoed proposed Federal rules today that would have required dealers to disclose major defects in used cars and state the extent of any outstanding warranties. The House voted 286 to 133 to join the Senate in rejecting the rules, which were proposed by the Federal Trade Commission. It was the first time Congress had exercised a legislative veto over the commission.

British troops are poised for a drive across East Falkland Island toward the Argentine garrison at Stanley despite the ''grievous'' loss of a destroyer and a merchant ship in air raids on Tuesday, Defense Secretary John Nott declared today. Mr. Nott told a sad and solemn House of Commons that the 3,500-ton destroyer Coventry had capsized after being bombed and strafed at the northern entrance to Falkland Sound and that the 15,000-ton container ship Atlantic Conveyor, requisitioned from Cunard for use as a makeshift aircraft carrier, had been crippled by two Exocet missiles. A total of 24 men were killed on the two ships, bringing known British losses to 100, he said, and about 25 others were wounded. Bleak Day for Britain British officials freely acknowledged that Tuesday, National Day in Argentina, had been the bleakest of the war for this country. But they said they had continued to chip away at Argentine air strength, shooting down four Skyhawks and a fifth, unspecified plane.