October 20, 1984

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.)