What was going on when I was born?

New York City is considering an $8 million contribution to the Metropolitan Museum of Art to construct its long-planned southwest wing. The wing would be built over the museum's public parking garage and would not encroach on Central Park. The $8 million, if approved, would be the largest of the capital grants given to the Met by the city for the museum's master-building plan. It would complete a financing package about which Met officials say they have the ''lion's share'' from a private donor.

An off-duty Transit Authority police officer was shot to death in the Bronx last night in a confrontation with two New York City police detectives that began with a dispute over traffic. The officer, 40-year-old Thomas Johnson, who had been with the transit police for 13 years, died at Lincoln Hospital early today after undergoing two and a half hours of surgery for a bullet wound in the neck, according to David Vickers, an administrator at the hospital. Sgt. Ed Burns of the Police Department gave the following account of the incident: At about 7 P.M. the two city detectives, Lloyd Wilson and Hugh Clark, who are assigned to the 40th Precinct detective unit in the Bronx, were driving a witness home in an unmarked police car. As they were driving up Cauldwell Avenue, a one-way street in the Melrose section, they encountered a truck between 158th and 156th Streets traveling in the wrong direction.

A witness in a Federal fraud investigation was found shot to death yesterday, and the police said she had probably been slain by the same gunman who killed three CBS employees Monday when they apparently went to her aid in a parking lot on Manhattan's West Side. Detectives said they believed that the man had stalked the murdered woman, Margaret Barbera, and that he was a professional killer. They also said her murder might be related to a Federal investigation into the embezzlement of about $6 million from a Manhattan diamond company. Another woman, Jenny Soo Chin, a friend and former co-worker of Miss Barbera, disappeared last January, and the police fear she also may have been killed. Woman Had Pleaded Guilty Miss Barbera, who was 38 years old and lived at 613 Grandview Avenue in Ridgewood, Queens, was found, shot in the back of the head, in an alley in lower Manhattan. She had pleaded guilty on March 29 to Federal conspiracy charges involving fraud and, according to court records, had agreed to cooperate with the United States Attorney's office in Manhattan in a continuing inquiry.

* Nan Bedford and May Lou Gorno have been elected partners of Tatham-Laird & Kudner Advertising, Chicago. * Cintra H. Huber has been appointed vice president of marketing for Phillips International, the auctioneer.

After raucous debate, a City Council committee yesterday approved new boundary lines for 35 Council districts. Council leaders hope the action, by the Committee on Rules, Privileges and Elections, will permit elections to be held in November. The 9-to-1 vote approving the lines, which came at 5:30 P.M., means the plan can be considered by the full Council at its next meeting, on April 27. Council leaders consider passage a virtual certainty. A meeting of the full Council yesterday could not consider the new lines because of a requirement that the bill ''age'' for eight days.

IN other, simpler times it was sufficiently satisfying for a horseplayer to have a successful, and therefore guiltless, day at the races, with success measured by whether the bettor won or at least broke even after an eight-race card. Horseplayers were single-minded people who went out to the track to bet, not to socialize, not to look at shrubbery, not to enjoy the air. If they ate at all it was on the run between races, and the fare usually consisted of sandwiches, hot dogs, hamburgers, snacks, coffee and doughnuts. The idea of eating bouillabaisse or a Linzer torte along about midcard would have been dismissed as so much gastronomic frippery. As would have Canadian bacon and shirred eggs with timed morning workouts, braised short ribs and buttered noodles with the daily double or whole suckling pig with the trifecta selections.