What was going on when I was born?

A senior Reagan Administration official said tonight that the 39 American hostages from a hijacked airliner were expected to be freed on Saturday after being taken from Beirut to Damascus. The Administration official declined to provide all the details of the transfer, saying that some might change overnight. But he said that the arrangement called for the 39 Americans to be taken over by Syrian authorities, who would promptly release them through an unidentified third party. Administration sources said the released hostages were likely to go to Frankfurt on their way back to the United States.

Federal officials learned that the 10,000 employees at a Government office building in lower Manhattan were drinking potentially unsafe water at least one month before informing anyone, Federal documents show. High levels of lead were discovered in early April at the 42-story building, 26 Federal Plaza, but employees were not told until May 13. They were then informed in a memorandum from the building manager that tests had found ''on a sporadic basis the safe level for lead is marginally exceeded.'' The memo advised them not to drink more than a quart of water from the building's supply a day. City water-safety and health officials were not immediately told, either, and they are now criticizing Federal officials for the delay and the manner in which the episode was handled.

The Government's index of leading economic indicators, which usually signals changes in the course of the economy, turned sharply upward last month, the Commerce Department reported today. Analysts saw the increase, of seven-tenths of 1 percent, as the first clear signal of what many have suspected for a few months - that the economy has seen the worst of a slowdown that began last summer and that it will grow a little more quickly as the year progresses. ''The economy is in a turning zone,'' said Lawrence A. Kudlow, a consultant here who was the chief economist at the Office of Management and Budget early in the Reagan Administration. ''We are bottoming out of a growth pause and we're moving toward reacceleration, but gradually, not precipitously.''

China, amid some ceremony, acquired a fleet of Cadillac limousines today. At a formal handover, Chinese officials lined up to accept the 20 dark blue limousines, described in Cadillac brochures as ''the car of the stars,'' each equipped with a built-in television set, refrigerator and bar. It was the kind of occasion that left Westerners with memories of Mao Zedong's China shaking their heads in disbelief. The ceremony was held only a short bicycle ride from the stadium where Mao's enemies were once paraded in duncecaps as ''capitalist roaders.''

Most of the American airliner hostages attended a banquet given by their captors at a luxury hotel Friday night amid indications that they would be leaving for the Syrian capital of Damascus within hours. Some of the hostages told reporters they had been led to believe that once they reached Damascus, they could be freed within two days. They characterized the lavish hotel dinner as a farewell party. ''We've been told we're going to Damascus,'' one of the hostages, Stewart Darsh, told reporters.

New York State's highest court ruled yesterday that Mayor Koch does not have the power to ban job discrimination against homosexuals by social-service agencies, including religious organizations, that do business with the city. The 6-to-1 decision by the State Court of Appeals invalidates part of Executive Order 50, the Mayor's 1980 directive against bias in hiring. The order has been in litigation for nearly a year, challenged by the Roman Catholic Archdiocese of New York; Agudath Israel of America, an Orthodox Jewish organization, and the Salvation Army on the ground that Mr. Koch had exceeded his powers as Mayor. City Charter Cited Writing for the majority, Chief Judge Sol Wachtler agreed, stating that ''because of the separation of powers delineated in the City Charter, the Mayor has no authority to initiate such a policy.'' The decision overturns a ruling by the Appellate Division of State Supreme Court and reinstates a Supreme Court order voiding the part of the executive order that bans discrimination on the basis of ''sexual orientation and affectional preference.''

President Reagan today strongly defended David A. Stockman, his budget director, following a report of an off-the-record speech in which Mr. Stockman said that tax increases may be the only way to curb the rise in the Federal budget deficit. In the June 5 speech, Mr. Stockman said a tax increase could be necessary if Congress does not act to reduce spending further or if the economy proves softer than the Administration is predicting. Mr. Reagan, asked about Mr. Stockman at a luncheon with community leaders in Chicago Heights, Ill., replied: ''He didn't say it. We know what he said. And the story is fallacious.''

Consumers are likely to begin paying as much as 3 cents a gallon more for leaded gasoline this weekend, as Monday's deadline for reducing the lead content in such gasoline approaches. Late this week Exxon, Sun, Amoco, and Mobil raised their wholesale prices for leaded gasolines in all or part of the country by 2 cents a gallon, and other oil companies are expected to soon follow. The 2-cents-a-gallon figure is widely accepted as the industry's increased cost of producing the lower-leaded gasoline. The other penny a gallon consumers may be paying represents dealers' profit. The reduction, to five-tenths of a gram of lead per gallon, from the current standard of 1.1 grams per gallon, to be followed on Jan. 1 by a further reduction to one-tenth of a gram, represents a major step in the Federal Government's goal of eliminating lead from gasoline - and eliminating the danger it poses to human health and the environment. Leaded gasoline is used by approximately 35 percent of the nation's 164 million motorists.

A top-ranking Afghan Army general has been killed by anti-Communist guerrillas, the official Kabul radio reported today. It said a General Ahmeduddin had been killed in a ''frontal clash with the bandits,'' referring to Moslem rebels fighting the Soviet-installed regime.

Leaders of the outlawed Solidarity union said today that about 50,000 workers at three major Warsaw factories would strike Monday to protest Government plans to increase meat prices by 15 percent.

Heavy rains caused by a typhoon lashed the main Philippine island of Luzon, flooding wide areas of Manila and leaving at least 28 people dead, officials said today. The flood was the worst to hit this city of 6.8 million in more than a decade.

Troops occupied one of Bolivia's provincial capitals today after demonstrators there set fire to an official car and stoned the homes of city and provincial administrators during a strike rally, officials said. They said soldiers moved into Sucre, the capital of Chuquisaca Province, where a mass rally was scheduled to discuss a four-day strike called by the authorities in the province, who have demanded greater local spending by the central Government. Interior Minister Gustavo Sanchez said the disturbances were caused by groups that wanted to sabotage the talks between the provincial authorities and the central Government.