What was going on when I was born?

A state appellate court ruled unanimously yesterday that a Bronx grand jury could listen to one of two tapes made by a surgeon at Montefiore Hospital and Medical Center to determine if the tape contained evidence implicating the physician in the attempted murder of his aide. The court reversed an earlier ruling by a justice of State Supreme Court in the Bronx who said both tapes were ''not relevant'' to the inquiry. Mario Merola, the Bronx District Attorney, has identified the surgeon, Dr. Richard G. Rosen, as the ''primary suspect'' in the near-fatal hammer beating of his aide, Clara Vanderbilt, on New Year's Eve. Dr. Rosen is vice chairman of the department of surgery at the north Bronx hospital.

The Food and Drug Administration asked Wyeth Laboratories today to begin an immediate, high-priority recall of a defective infant formula. Hours earlier, a company spokesman testified at a House subcommittee hearing that the company had known about the problem for possibly 10 days but had been prevented from issuing a recall by governmental procedures. The Federal agency involved later denied that that had been the case. An unknown quantity of the infant formula, sold under the brand name SMA, is deficient in an essential nutrient, vitamin B6. The Wyeth spokesman, Charles F. Hagan, testified that the problem had been caused by a worker's mishandling of vitamins.

Despite the Administration's investment tax incentives, American business is scaling back its 1982 spending plans in real terms by 1 percent from last year's level, the Commerce Department reported today. The results of the January-February survey were a disappointment to Administration officials, who count on capital investment to help bring the economy out of the recession. The survey showed that businesses expected sales to increase 9.9 percent this year, better than the 8.2 percent growth of last year. But plans for capital improvements have been cut back further from the reduction of one-half of 1 percent that was expected in the November-December survey.

One-hundred-fifty black cowboys and cowgirls from across the country - all professional rodeo competitors - will demonstrate riding and roping skills today at 11 A.M. and 8 P.M., tomorrow at 2 and 8 P.M. and Sunday at 3 P.M. at the 369th Infantry Regiment Armory, Fifth Avenue and 143d Street in Harlem. The participants in this first ''Bill Pickett Memorial African American Cowboy Circuit'' will ride bucking broncos bareback, wrestle steer, ride bulls and wild horses, and race in and around barrels. Also on the program will be a pageant on the history of black cowboys dating back to the Old West. Some of the proceeds are to be used to start an ''Urban-Western'' program for black youths and adults to teach horsemanship. Tickets are $6 to $15. Information: 293-5882. LATIN FILMS AT N.Y.U. ''Chac,'' a 1975 movie based on Mayan mythology and directed by Ronaldo Klein, is being shown tonight with English subtitles in New York University's free Spring Festival of Latin American and Caribbean Films. Offered Fridays at 6:30 P.M. in Room 703, 100 Washington Square East, the films - from Brazil, Mexico, Chile, Cuba, Colombia and the United States - include both features and documentaries. Information: 598-3395.

JOHN CAGE is still very much with us, but already he has become an icon on the landscape of our cultural life. As the unchallenged father figure of American experimental music, Mr. Cage wields an influence that extends far beyond sound alone to embrace the graphic arts, poetry, philosophy, religion and even mycology, the branch of botany that deals with fungi, in this case mushrooms, on which the composer is a foremost authority. Indeed, the entire American avantgarde would be unthinkable without Mr. Cage's music, writings and genially patriarchal personality. This year will mark Mr. Cage's 70th birthday, which falls on Sept. 15. But even now the drums are beating in anticipation of the day, and Mr. Cage finds himself jetting all over the world for celebrations of his achievements. The biggest, most ambitious and widest ranging of these festivities in New York will take place all day tomorrow - a free, 13-hour ''Wall-to-Wall John Cage and Friends'' marathon at the venturesome Symphony Space at Broadway and 95th Street (864-1414). The event will begin at 11 o'clock in the morning, end around midnight and be open to any and all, first-come, first-served. In addition, seven hours will be broadcast live, off and on throughout the day, on WNYC-FM (93.9 on the dial), and part of the program will be filmed for inclusion in a Cage documentary.

The BankAmerica Corporation's problem loans surged to $1.6 billion in 1981 from $577 million at the end of 1980, the bank holding company said yesterday in its fourth-quarter analytical report. It attributed the sharp rise to the recessionary environment. A significant part of the rise was attributed to difficulties encountered by smaller businesses, especially to those in the real estate business.

Stockholders of the Marathon Oil Company today approved a $6 billion merger of the nation's 17th-largest oil company with the United States Steel Corporation. Smiling broadly, Harold W. Hoopman, Marathon's 62-year-old president, stepped to the microphone before stockholders and accepted a report from independent election inspectors that more than two-thirds of Marathon's 58.7 million shares had voted in favor of the merger. A final tally will not be ready for several days. However, an unofficial estimate placed the shares voted for U.S. Steel at 43 million, including 30 million that the steelmaker cast for itself.

State Comptroller Edward V. Regan, who has been the leading candidate for the Republican nomination for Governor of New York, has decided to drop out of the gubernatorial race and seek re-election as Comptroller, three of his top aides said yesterday. The move by Mr. Regan, which came after nearly 24 hours of meetings and conversations in Manhattan that ended at 3 A.M. yesterday, threw the Republican Party in the state into disarray. Even Republican leaders acknowledged that the Regan decision increased Democratic chances of retaining control of the most powerful office in the state. ''It's all over,'' said a top aide and longtime friend of Mr. Regan. ''He's going to get out,'' said a close adviser. The Regan decision came only four days after the Republicans lost a Senate contender, Bruce M. Caputo. He had quit after a furor raised by his claim on several occasions that he had served in the Army when he had actually been a civilian working in the Defense Department and thus deferred from active military service.

An article in Business Day Monday incorrectly reported United States oil imports from Arab countries. The United States receives about one-tenth of the oil it consumes from Arab countries.

Articles in Business Day Wednesday and Thursday incorrectly re ported the statements of William Agee, chairman and chief executive of the Bendix Corporation, regarding his relationship with Mary E. Cunning ham. Mr. Agee has consistently stated that there was no romantic relationship at the time Miss Cunningham was employed by Bendix.

The British Government announced today that it had decided to buy from the United States a costly and advanced new missile system for its nuclear submarine fleet so Britain would have an independent nuclear deterrent into the next century. The Trident 2 missile system will cost $14 billion over 18 years, the Government said, and will replace Britain's Polaris missiles in its fleet of nuclear submarines, which will also be replaced. It is the same missile system the United States Navy is to begin using around 1989, and the decision to deploy it in Britain was welcomed in letters released here from President Reagan and Secretary of Defense Caspar W. Weinberger.

President Jose Lopez Portillo of Mexico said Wednesday night that better relations between the United States and Cuba would ease tensions throughout the Caribbean Basin and facilitate solutions to the crises in El Salvador and Nicaragua. ''I am absolutely certain that Cuba is willing to negotiate all the questions worrying to the security of the United States,'' Mr. Lopez Portillo said. He also insisted on the need for negotiations between the United States and Nicaragua's Sandinist Government and between the warring factions in El Salvador. ''I think it would be irrational not to exhaust all possibilities or negotiated solutions,'' he said in a meeting with A.M. Rosenthal, the executive editor of The New York Times, and this correspondent.