What was going on when I was born?

A senior officer in the largest Nicaraguan rebel group today disputed White House explanations of a Central Intelligence Agency manual on guerrilla warfare. The booklet, prepared for Nicaraguan rebels, offers advice on how to kidnap and kill Nicaraguan Government officials. On Thursday a senior White House official told reporters that the primer, which was made public this week, was a first draft that was later revised before distribution. ''Once it was seen,'' the official said, ''everything that was not policy was deleted from it.''

The United States Embassy here, responding to continuing terrorist threats, has begun evacuating dependents and ''nonessential'' personnel and is considering reducing its staff to a minimum. Diplomatic sources close to the situation said a reduction of the already scaled-down American presence in Lebanon was one of several security options under study. In Washington, a State Department spokesman said all the American dependents in Beirut - a total of six - had been ordered to leave the country. Reagan Signs Bill The developments came as President Reagan signed legislation allocating $366 million to enhance security precautions at United States embassies worldwide. The Administration asked for the funds after the bombing Sept. 20 of the United States Embassy near East Beirut, and the measure won quick approval in Congress.

As Sunday's foreign policy debate between the Presidential candidates nears, voters who have made up their minds back President Reagan's approach, while undecided voters are less impressed by his policies, the latest New York Times/CBS News Poll indicates. By a margin of 46 percent to 40 percent over all, those polled approved of the way Mr. Reagan is ''handling foreign policy.'' Forty-eight percent of those who said they had made up their minds on whom to vote for approved, while 41 percent disapproved. But those who said they had not decided whom to vote for - a key group that both sides hope to sway - disapproved of the President's foreign policy, by 36 percent to 32 percent. Margin of Error There is a sampling margin of error in the poll of plus or minus 3 percentage points, except in the case of smaller groups, such as undecided voters, in which the margin for error is 7 points.

Associate Justice William H. Rehnquist said today that any President's efforts to leave a lasting ideological mark on the Supreme Court were likely to fail. ''There is no reason in the world'' for a President not to try to ''pack'' the Supreme Court with Justices who agree with him, Justice Rehnquist said in a speech to a law school audience in Minneapolis. But throughout the country's history, he said, such efforts have been at best only partly successful. Unexpected legal developments, personal antagonisms, the Court's tradition of independence as well as ''blind chance'' all tend to frustrate a President's ability to predict the performance of Supreme Court nominees, he said.

''While both Presidents and judicial nominees may know the current constitutional issues of importance, neither of them are usually vouchsafed the foresight to see what the great issues of 10 or 15 years hence are to be.'' - Associate Justice William H. Rehnquist. (9:5.)

City and state tax agents, backed by police officers, raided the Bulgari jewelry store in the Pierre Hotel yesterday in what they termed a continuing investigation into sales-tax evasion. As customers browsed at displays of $2,500 wristwatches and diamond and gold necklaces worth many times more, agents with a search warrant seized store records. For months, tax agents have been compiling evidence that retailers of jewelry, furs and other luxury merchandise systematically join customers in efforts to evade the 8.25 percent city and state sales tax. By evading the tax, a customer could save $825 on a $10,000 necklace.

The nation's economy grew at a surprisingly slow annual rate of 2.7 percent from July through September, the Commerce Department reported today. Growth of the gross national product, the most comprehensive gauge of the economy's performance, was substantially weaker int he third quarter than the 3.6 percent annual rate that the Government first estimated last month. The pace was also sharply below the 10.1 percent rate of growth inthe first quarter and the 7.1 percent in the second. Moreover, it was the slowest rate since the first months of 1983, when the recovery started accelerating.

Three United States military advisers flew into this rebel-dominated area Friday and marched to this town while fighting was taking place on a nearby hill between Salvadoran Army and rebel combat units. The town had been cleared of the rebels a few hours earlier in an assault by the elite Atlacatl battalion. The presence of the Americans, all assigned to the United States Embassy in San Salvador, raised questions about the role of American military advisers in El Salvador and the rules that govern their activities in areas of actual or potential conflict. These rules, which have been the subject of Congressional debate in the past, appear to have become more flexible, according to senior American diplomats in San Salvador.

Four Americans, all employees of the Central Intelligence Agency, were killed today when their unarmed airplane crashed on a surveillance mission over El Salvador, Reagan Administration officials said this evening. The officials said there was no indication the plane had come under fire. They said the crew was helping the Salvadoran Government by looking for signs of guerrilla offensives and of arms smuggling. The crew consisted of one C.I.A. officer and three contract employees of the agency, the officials said. The deaths are the first known agency casualties in the conflict in Central America.

It was 40 years ago Saturday that Gen. Douglas MacArthur honored his famous pledge - ''I shall return'' - by landing here with 200,000 troops. Today this palm-fringed beach is a picture-postcard version of tropical calm as local children play in the surf and the horizon is dotted with a few fishing boats against an azure sky. But on A-Day, Oct. 20, 1944, this portion of the eastern shore of Leyte island, code-named Red Beach, presented a very different picture. ''As we came into the beach, there were shells exploding all over the place,'' recalled Paul Austin, an infantry commander who came ashore in the second wave of the landing.

The Justice Department announced yesterday that a second naturalized American citizen had surrendered his citizenship and left the United States for West Germany rather than contest charges involving Nazi war crimes during World War II. The department said the case involved a man identified as John Avdzej, a 79-year-old retired draftsman from Roselle Park, N.J. He was said to have admitted ''misrepresentations and concealments'' regarding his service as regional mayor of Stolpce in Nazi-occupied Byelorussia. During that time, the Government said, nearly all the Jews and many Polish civilians there were slain.

Secretary of State George P. Shultz said today that the United States was ready ''for a major effort'' to ease tensions with the Soviet Union in coming years. If Moscow reciprocates, he said, it could be ''a most productive period in Soviet- American relations.'' Mr. Shultz, in his most partisan speech since taking office, said the ''last four years have put the building blocks in place for a promising and productive second Reagan term.'' The Secretary, who until now contended he was not taking part in the Presidential campaign, spoke to the Los Angeles World Affairs Council. The text of his address was distributed here.