What was going on when I was born?

Air-conditioning units on New York City buses, both old and new, require such a high degree of maintenance that transit officials say they are fighting a losing battle to keep buses cool this summer. The problem is so extensive, according to one top bus official, that the city would be wise to forget about air-conditioning its buses altogether. ''Go over to Europe,'' said the official, Charles J. Milau, general superintendant for maintenance. ''Do you see airconditioning on those buses? Of course not.''

Mayor Koch said yesterday that he would support efforts to make single-room-occupancy hotels ineligible for the benefits of a taxincentive program for real-estate developers. The Mayor's statement came less than three weeks after the State Legislature decided not to approve extension of the program, known as J-51, which also covers residential apartment buildings. Among other reasons, the program has been controversial because it has displaced thousands of tenants from single-room-occupancy hotels.

The nation's gross national product rose in the second quarter at an annual rate of 1.7 percent after adjustment for inflation, the Commerce Department reported today, the first upturn in this key indicator since last summer. The increase surprised many economists, leaving them divided over whether the recession was over and what the outlook might be for a recovery. Some economists who had expected a small improvement in the G.N.P, which measures the total value of the nation's goods and services, were surprised that the increase was much larger. Others, who recently predicted a decline, contended that the recession was not over, despite the increase for the April-to-June quarter.

The Continental Illinois Corporation, the nation's sixth-largest banking organization, announced yesterday that it lost almost $61 million in the second quarter. Bankers said it was the biggest quarterly loss by a major banking company in recent history. The loss was largely a result of the company's dealings with the Penn Square Bank of Oklahoma City, which failed last July 5. Continental was the second major bank to have announced a loss this week. On Tuesday, the Chase Manhattan Corporation, the nation's third-largest, said that it had lost $16.1 million in the April-June period, also partly because of a relationship with Penn Square. It was the first time, at least in recent history, that any of the nation's 10 largest banks reported a quarterly loss.

In their first debate of the primary campaign, the three Republican contenders for the United States Senate from New York yesterday criticized each other and the Democratic incumbent, Senator Daniel Patrick Moynihan. One of the candidates, Whitney North Seymour Jr., accused the Senator of ''scaring the dickens out of senior citizens'' and ''an outrageous crying of wolf'' in pointing up his efforts to prevent Social Security cutbacks. Another contender, Assemblywoman Florence M. Sullivan, described Senator Moynihan as ''an intellectual elitist who has been living in an ivory tower - who has been conducting himself more like a man of letters, a professor of whatever, than he has as the United States Senator representing the interest of the people of this state.'' The third candidate, Muriel Siebert, criticized the Senator for what she said was his failure to help her, as State Superintendent of Banks, in her efforts to help savings banks on the brink of closing their doors.

BOOKSHELVES have always been a necessity for storing ever-growing collections. But recently for some designers and architects, those ranks of shelving have proved a creative way to manipulate interior spaces: to create new rooms, accent existing architecture or conceal structural flaws. ''Bookshelves can often make a room seem more spacious,'' said Melvin Dwork, an interior designer who created a wall of bookcases that conceal access to a guest closet and bathroom in the apartment of Nadia Stark. ''Originally the room looked chopped up with two doors placed close together in such a small space,'' Mr. Dwork said. ''The bookshelves also give the combination guest room and library a three-dimensional feeling and an added sense of texture and color.''

Gen. Wojciech Jaruzelski, the Polish leader, announced today that more than 1,200 people detained under martial law were being released, and that martial law itself could be suspended by the end of the year if tensions subsided. In a speech to Parliament, he also reported that the long-debated visit by Pope John Paul II, to which many Poles had looked forward, would not take place in August and that it might be rescheduled for next year if life in Poland returned to normal. A Government spokesman said Lech Walesa, the head of the Solidarity labor union, who has been in solitary detention for seven months, was among 637 men who would remain interned. It was generally assumed that most of his associates would continue to be detained.

A dispatch from Quito yesterday about Ecuador's economy was accom- panied by an incorrect photograph. It actually showed Bogota, Colombia.

The House of Representatives today narrowly defeated a measure that would have stopped spending for production of the MX missile. Hours later, the House also decided a heavily lobbied contest between the Boeing and Lockheed companies by upholding a Pentagon request to purchase 50 Lockheed C-5 cargo planes for military airlift. The votes, both of which backed positions held by President Reagan, came as the House debated a long list of amendments to a bill authorizing 77.1 billion in new spending authority for military procurement, research and development and military operations and maintenance. On both key questions the vote margins surprised many members.

The Republican majority in the Senate defeated several attempts by Democrats today to change the tax increases and spending cuts brought to the floor by the Finance Committee. The voting appeared to set the stage for Senate approval Thursday of the bill largely as it was written, which would be a victory for the Reagan Administration. In the House, the ranking Republican on the Ways and Means Committee, Representative Barber B. Conable Jr. of upstate New York, conferred for the second time in 24 hours with the Democratic chairman, Representative Dan Rostenkowski of Illinois, on a bill to be drafted in the House, which traditionally originates tax legislation. ''We're not in great disagreement,'' Mr. Conable said.

Secretary of State George P. Shultz has declared that he favors no approach to Middle East negotiations other than those called for in the 1978 Camp David accords for granting self-rule to the Palestinians living in the Israeli-occupied West Bank and Gaza Strip. In written replies to questions submitted by senators at the time of his confirmation hearing last week and made public today, Mr. Shultz also said that, although there might appear to be some shortterm advantages in threatening to withhold aid from Israel, ''pressure and threats are not in my mind the best way to bring about stable and lasting solutions.'' During his confirmation hearings, Mr. Shultz made an urgent plea for resolution of the Palestinian problem but made only passing reference to the Camp David accords. Bechtel Ties Cited Even though he was careful to balance his statement at his hearings with strong support for Israel, his remarks created an impression, particularly in the Arab world, that he was considering an approach other than Camp David to advance the peace process.

The American subsidiary of one of Japan's huge trading companies pleaded guilty today to charges of fraud and making false statements in a conspiracy to sell imported steel below allowable prices. Mitsui & Company (U.S.A.) agreed to pay $11 million in civil penalties and $210,000 in criminal fines, the largest criminal-civil settlement in the history of the Customs Service, according to United States Attorney Joseph Russoniello. Federal officials said they had been investigating Mitsui's trade practices since 1980. The guilty plea was entered at a hearing before Judge Marilyn H. Patel in Federal District Court just one day after Mitsui and three current or former employees had been named in a 21-count Federal grand jury indictment.