President Reagan, seeking to spur movement in the deadlocked talks on troop withdrawals from Lebanon, said today he will not approve delivery of advanced F16 jet fighter-bombers to Israel while Israeli forces continue to occupy Lebanon.

Reagan had refused for months to say what action he intended to take about the F16 deliveries, and the administration had turned aside all questions about the situation by saying the president had it under consideration.

Today, answering questions after a speech here, Reagan was asked why the United States had not sent the planes to Israel to counter the Soviet Union's delivery of SAM5 surface-to-air missiles to Syria, which has an estimated 35,000 troops in northern and eastern Lebanon. He answered:

"You must realize that under the law--the law exists now--those weapons must be for defensive purposes. And this is again one of the obstacles presented by the stalemate in Lebanon. While those Israeli forces are in the position of occupying another country . . . we are forbidden by law to release those planes . . . and it's as simple as the other forces returning to their own countries and letting Lebanon be Lebanon."

His response left some confusion about why he was stating a policy about the F16s at this time. Despite Reagan's contention that the law bars him from sending weapons to Israel while its forces are in Lebanon, the Pentagon last week notified Congress of its intention to sell 200 Sidewinder air-to-air missiles worth about $16 million to the Jewish state.

However, the Sidewinder deal was announced at a time when U.S.-Israeli relations appeared to be improving as the result of talks in Washington in mid-March on a withdrawal from Lebanon agreement and because of Israel's decision to share with the United States intelligence information it obtained from the capture of Soviet equipment from the Syrians during the fighting in Lebanon last summer.

More recently, though, U.S. officials have made clear that the optimism about a Lebanon breakthrough that had been expressed after the Washington talks between Israeli Foreign Minister Yitzhak Shamir and Secretary of State George P. Shultz has declined. Israel, the officials said, has continued to insist on the right to a residual military presence in southern Lebanon.

The officials left no doubt that the latest turn in the Lebanon talks has U.S. negotiators frustrated and irritated at the Israeli government. But, officials at the State Department in Washington stressed privately tonight that they had no information to confirm that the president's remarks were intended as a signal of this annoyance.

There also was some speculation that Reagan's comments may have been aimed in part at Jordan's King Hussein and Palestine Liberation Organization leader Yasser Arafat who are expected to meet shortly for further discussion of whether the PLO would give Hussein a green light to enter the expanded Mideast peace talks Reagan called for last Sept. 1.

While the president's remarks today may have psychological effects on Israel and are likely to cause new tensions in U.S.-Israeli relations, they will not have any immediate impact on the Middle East arms balance. Delivery of the next group of F16s, part of a sale of 75 planes arranged in 1975, had not been scheduled to begin until 1985.

In other comments, Reagan defended his decision to seek new limitations on contacts between government officials and reporters, saying that some stories in the press that reveal private negotiating positions are harmful to U.S. interests.

Two weeks ago the administration proposed guidelines to force government workers to take oaths against disclosing information, and said it would use polygraph tests to see if federal employes had spoken to reporters.

"What we are trying to control is what seems to be the favorite game of Washington, even more popular than the Redskins, and that is leaks," the president said. He contended that some leaks, frequently from lower-ranking bureaucrats, are "incomplete or misinformation" and have harmed relations with U.S. allies and made more difficult the task of negotiating arms reductions with the Soviet Union.

"All we have proposed is methods of intercepting the leaks from the government itself to the press. But I do not believe that we are making it difficult at all. As a matter of fact, I have increased the amount of time that I am going to spend with the press," Reagan said.

"And I just think," he added to loud applause from his audience at the Beverly Hilton Hotel, "the press must recognize it, too, has a responsibility for the welfare of the nation."