What was going on when I was born?

In a new and unorthodox ploy to encourage its customers to stay loyal to Ma Bell, the American Telephone and Telegraph Company said yesterday that it would give its residential customers discounts on everything from microwave ovens to airplane tickets. The phone company's plan, similar to incentive programs used on and off by gas stations, airlines and even Citibank and American Express, will be available to nonbusiness customers who run up long-distance bills of more than $15 a month. The amount of the discounts increases as customers talk longer. And with cut-rate competitors like the MCI Communications Corporation and GTE-Sprint already taking away customers, the telephone giant showed yesterday that it was wasting no time with its response: On Wednesday, it began mailing out 25 million copies of a glossy, 14-page catalogue brimming with color pictures of products and services available at a discount to A.T.& T. users. ''This is a reward for our best customers, another reason for them to stay with A.T.& T.,'' said John Smart, the vice president of marketing for A.T.& T. Communications, the unit that runs the company's long-distance services.

A front-page photo caption yesterday incorrectly identified the location where residents were viewing an annular eclipse. The photo was made in Houston.

''Philosophically, a group of us on the board thought that smokers had rights, too, but afterward I talked to the staff about scheduling problems, enforcement and the sneak smoker.

Phibro-Salomon Inc., the big New York commodity trading and investment banking house, said yesterday that it was no longer considering splitting up the company. Only 10 days ago, Phibro said that it was studying whether to sell its commodity trading operations, except oil, to a group of executives and employees. Yesterday, in a one-sentence statement, Phibro said only that the study had been ''terminated.'' Top executives would not elaborate, but insiders said that while no price had ever been proposed officially, the two main factions within the company could not agree on one. One insider, who asked not to be identified, said that he thought the commodity trading operations being sought were worth at least $750 million.

A Nicaraguan insurgent leader wounded Wednesday night in a bomb attack that killed five people was taken into Costa Rican custody today as the Government apparently sought to stress its official neutrality in Central American conflicts. The bomb, which wounded 27 people, exploded during a news conference being given just inside the Nicaraguan border by the rebel leader, Eden Pastora Gomez. Mr. Pastora, whose Revolutionary Democratic Alliance is based in Costa Rica, was brought for treatment to a San Jose clinic, where he was placed under police guard. ''He is under the control of the Public Security Ministry,'' the Information Minister, Armando Vargas, said. ''Later it will be decided what his destination should be.''

A reporter was interviewing a group of students from the American University of Beirut the other day, and at the start of the conversation he asked them to give their ages. Before anyone else could respond, one girl, named Rima Koleilat, whispered softly and sadly under her breath, ''We are all 100 years old.'' Some days it really must seem that way for Lebanon's ''lost generation'' - those who have grown up during the last nine years of civil war. They were just waking up on the world, just starting to read the newspapers, when the war blew away their adolescence before they even knew it was gone. ''We've been given a crash course in being human beings,'' said Hana Abu Salman, a 23-year-old graduate psychology researcher at the American University. ''Bingo. Suddenly everything was life and death and you grew up with it real fast. We lost that feeling of being carefree. I think I have been serious since I was 14.''

Even at its quietest, the block of 42d Street between Seventh and Eighth Avenues is filled with disquieting voices. They are raspy, thick, shrill or emotionless, shaped, at least in some part, by life on what by almost every account is midtown's most crime-filled and, for many, its most forboding block. ''There's a saying on this block - over here, you never die,'' said James Rodriguez, a 22- year-old standing outside a game room in the Eighth Avenue subway arcade. No matter how down-and-out or how strung out on drugs, ''you can always make money on this block,'' he said, explaining why even at 11 P.M. on one of the coolest nights in the past month, crowds of teen-agers and well-worn older men were spilling out of the game room and into the arcade. They call the arcade ''the Hole,'' and the police say it is the biggest incubator of crime on the block.

-time penny-arcade owner and an ex-glove salesman from Poland were once involved in the creation of a giant. The arcade owner was Marcus Loew (born in 1870 in New York City of Austrian immigrant parents), and by 1912 his arcades had become Loew's Theatrical Enterprises, and he owned 400 movie theaters. In 1920, he bought the Metro Picture Corporation to provide films for his theaters. Four years later, in 1924, Loew got a controlling interest in the Goldwyn Picture Corporation (whose co-founder was the former glove salesman Samuel Goldwyn, originally Samuel Goldfish, born in 1882 in Warsaw) and Louis B. Mayer Pictures (run by the former scrap merchant, originally Eliezer Mayer, born in 1885 in Minsk), and the film studio giant Metro-Goldwyn-Mayer was born. M-G-M is now 60 years old, and in honor of its 60th anniversary, a ''Diamond Jubilee Series'' of 57 of its most famous movies will be shown at the Regency Theater, beginning Sunday and continuing through Aug. 11.

The Civil Aeronautics Board tentatively agreed today to ban all smoking on commercial flights of less than two hours. But soon afterward the staff convinced the board chairman, who favored the rule, that it would cause insurmountable problems. ''It is apparent they are not going to be adopting this two-hour rule,'' said Teodor R. Lopatkiewicz, the board's spokesman. The rule the board tentatively adopted would have barred all smoking on 85 percent to 90 percent of domestic flights, including the popular shuttles linking New York with Washington and Boston.

Costa Rica took into custody a Nicaraguan rebel leader wounded Wednesday night in a bomb attack. The Government's move was apparently designed to stress its official neutrality in Central American conflicts. Five people, including a United States journalist, were killed and 27 were wounded when a bomb exploded during a news conference being given by the insurgent leader, Eden Pastora Gomez. (Page A1, Column 6.) The mines deployed recently against shipping in Nicaraguan harbors were constructed by the C.I.A. with the help of a United States Navy laboratory, according to Reagan Administration officials. In an interview four days ago President Reagan said the mines were ''homemade.'' (A4:3-6.)

The head of the Federal mass-transit agency said today that New York City was ''obliged to reimburse'' the Government $56 million because the city's Transit Authority had permanently withdrawn its fleet of Grumman Flxible buses. The official, Ralph L. Stanley, administrator of the Urban Mass Transportation Administration, told a House subcommittee that he was asking for payment by July 1. The panel - the Subcommittee on Investigations and Oversight of the Public Works and Transportation Committee - is investigating the Transit Authority's decision to remove the buses on the ground that they were unsafe. Under questioning today, Mr. Stanley said he had no evidence to support the Transit Authority's conclusion that the buses were not safe.

Providing new evidence that the national economic recovery is slowing, the Commerce Deaprtment said today that its main economic forecasting gauge rose a modest five-tenths of 1 percent in April. The increase in the index of leading indicators, which is intended to forecast the nation's economic health six to nine months in advance, resumed its nearly two-year upward trend after having dropped by one-tenth of 1 percent in March. However, the April increase was much smaller than the gains that were typical much of last year.