What was going on when I was born?

New York City's public-school system opens this week with two new high schools, $215 million more to spend than last year, a Chancellor who is still in his rookie year and some new teachers who have never taken an education course. But for the city's 936,800 students, the novelties will mean little next to the verities of a first day of school. Most students will probably once again feel that keen mingling of eagerness and anxiety that September evokes. Many teachers, too, will face the clutching sensation of meeting all those new faces - students who could make their year an agony or could provide that deep gratification of having touched a young soul that is so special to the profession.

The Central Intelligence Agency believes two of the men killed when Nicaragua shot down a rebel helicopter Saturday were American mercenaries, Senator Daniel Patrick Moynihan said today. Mr. Moynihan, a New York Democrat who is vice chairman of the Senate Select Committee on Intelligence, said the C.I.A. had told him that the two were not directly or indirectly associated with the agency, which has supported the Nicaraguan rebels since 1981. Mr. Moynihan said he had been told that the helicopter was on a reconnaissance mission after a rebel ground attack on a Nicaraguan military outpost. There have previously been no known American deaths in Nicaragua associated with the three-year-old rebel fight against the Sandinista Government. A primary concern in Congress about American support for the rebels has been the possibility that C.I.A. employees or other Americans would become involved in the fighting. Some members of Congress have warned that the loss of American lives in the conflict could draw the United States into a more direct and extensive military involvement. The Reagan Administration, partly in response to these concerns, has a standing policy that American Government employees, or anyone working on contract for the Government, shall not take part in any activities inside Nicaragua.

Under a steady downpour and the watchful eye of hundreds of armed soldiers and policemen, tens of thousands of Sikhs jammed a shrine here today for an anti-Government rally at which religious leaders called for a mass march to liberate their holiest site from the army occupation. Thrusting their arms into the air, the Sikhs also shouted their approval for a merger of conflicting Sikh political factions into a unified party, the Akali Dal. The meeting here in Punjab state, described as a world Sikh convention, was designed to ratify a broad anti- Government program that many here believe could lead to sharper confrontations with supporters of Prime Minister Indira Gandhi. In June, Mrs. Gandhi ordered an army assault on the Golden Temple, the Sikhs' holiest shrine, to dislodge a group of Sikh militants.

The bus left Georgia early Saturday morning, carrying 40 people headed to New York City to help rehabilitate a building on the Lower East Side. By late afternoon, appetites were growing. ''Jimmy, can you pass the cookies?'' asked Betty Pope. The man with the pink sweatshirt wrapped around his shoulders turned in the narrow seat and handed over a box of homemade pecan crunchies, not without stopping to take one for himself. ''Thank you, Mr. President,'' Mrs. Pope said.

The President's advisers say he intends to tone down his campaign attacks and shift to positive themes. Page 9. MINNEAPOLIS, Sept. 2 - Walter F. Mondale charged today that the Republicans had ''raised doubts whether they respect the wall our founders placed between government and religion.'' In a free-swinging five-minute radio speech broadcast nationwide, the Democratic Presidential nominee warned that mixing religion and politics ''will corrupt our faith and divide our nation.''

Listen to the voices at the National Tennis Center, a 16-acre asphalt jungle in Queens and home of the United States Open, the only major tournament played in a public park. They are different from the hushed voices heard when this tournament was played at the Casino in Newport, R.I., at the Germantown Cricket Club in Philadelphia or at the West Side Tennis Club in Forest Hills, Queens. They are the voices of a sport that is no longer limited to the grass courts of country-club settings, no longer played exclusively by privileged athletes and before privileged crowds. They are New York voices, with the accents of New York's neighborhoods, and sometimes they are loud and brassy.

In one room, a group of 3-year-olds are learning about Mexico; some are inspecting a map and a story book with a young teacher, while others glue orange and yellow crepe paper to a pinata they are making from a brown paper bag. In another room, children 4 and 5 years old are learning about the Plains Indians; they have made paper tepees laced with yarn and are stringing beads on Ojibway vests. Interspersed with those activities are singing, dancing, playing in the sandbox, hanging on the jungle gym, napping, finger-painting and other such diversions. It is a typical morning at the Hallie Q. Brown Community Center, a day-care facility in St. Paul that serves children from lower-income as well as more affluent familes. Parents pay $50 a week for each child at the center. At two other day-care facilites nearby, the cost is the same, but there are striking differences in the programs and types of care offered, as well as the physical environments in which the children typically spend 50 hours a week.

Shimon Peres and Prime Minister Yitzhak Shamir reported tonight that ''serious obstacles'' were blocking the formation of a bipartisan Israeli government. The two leaders, representing the nation's major political blocs, were terse and grim-faced as they left a two-hour meeting. The indications that the negotiations were faltering appeared to represent the most serious setback since coalition talks began a month ago. They parted without setting a new meeting, but said ''further contacts'' would be attempted. Neither Mr. Peres, who heads the Labor Alignment, nor Mr. Shamir, leader of the Likud bloc, would say how or when those contacts would be maintained.

Union members and leaders are approaching Labor Day 1984 with a growing feeling that the balance of power in the workplace has shifted dramatically in favor of employers. From the A.F.L.-C.I.O.'s president, Lane Kirkland, to striking muffler makers in Toledo, to packing plant union organizers in Georgia, union members say that decades of grudging mutual tolerance, encoded in labor laws and ritualized in collective bargaining, have broken down. Uncertainty About Solutions There is no consensus within the movement about how to reverse labor's fortunes. Some prescribe greater cooperation with management; others call for a return to militance. Some see the future in unionizing bank tellers and secretaries; others are more concerned about sheltering steel and automobile plants from foreign competition. Many want to change the laws governing labor relations; a few argue they should be repealed outright, returning ''the law of the jungle.''

Prime Minister John N. Turner, leader of the Liberal Party, campaigned vigorously in his home district today, telling audiences that he thought there was still time to turn the tide against his conservative challenger. But with two days to go before the elections on Tuesday, Brian Mulroney, leader of the Progressive Conservative Party, appeared to be maintaining his large lead over Mr. Turner. If the polls are correct, Mr. Mulroney seems likely to become only the third head of a majority Progressive Conservative government during this century. Political commentators say his strength is the result of the public's weariness with the governing Liberals, new Tory strength in Quebec and an expertly honed campaign.

Former Secretary General Kurt Waldheim, assessing the role of the United Nations, says the organization has moved into areas in which ''clashing interests threaten to tear it apart.'' ''The United Nations has fallen upon hard days,'' Mr. Waldheim wrote in an article made public here today. ''It goes through its paces in a workaday routine that is increasingly ignored or condemned and that threatens to become increasingly irrelevant in the real world,'' he said. ''It is moving into fields of operation in which clashing interests threaten to tear it apart.''

Umaru Dikko, the former Nigerian Cabinet minister found drugged in a crate at an airport after being kidnapped two months ago, said in an interview published today that he had been warned he might be in danger. In his first interview since the abduction, Mr. Dikko, a former Transport Minister, told The Sunday Times: ''Of course I had been told that my life was in danger.