The administration yesterday reiterated President Reagan's warning that American F16 fighter-bombers will be withheld from Israel until Israeli forces leave Lebanon. But U.S. officials, apparently seeking to ease the impression of a new get-tough attitude toward Israel, insisted that the president was only restating a policy in effect since the invasion of Lebanon last June.

The F16 dispute, which could cause new U.S.-Israeli tensions, broke out Thursday when Reagan, speaking in Los Angeles, said he was legally barred from approving the sale of 75 F16s because the presence of Israeli forces in Lebanon violates an agreement that American arms can be used only for defensive purposes.

After reporters raised questions about whether Reagan's interpretation of the law was legally correct, White House spokesman Larry Speakes, speaking in Santa Barbara, Calif., said: "The legalities of it are that we have concern that the invasion of Lebanon may have violated the spirit of the law . . . . It is our view that while Israeli forces remain in Lebanon that we have concern arising out of the fact and we do not believe it would be consistent with the spirit of the law to go ahead" with the sale.

In Washington, State Department spokesman Alan Romberg, stressing that the president was not saying the planes will be withheld from Israel permanently, said Reagan had secretly told Congress last July that Israel might be in violation of the law.

Reports from Israel said that officials there had been angered by Reagan's remarks. However, a statement issued by the Israeli embassy here took a low-key approach, defending the incursion into Lebanon as "acts of legitimate self-defense." The embassy added that the F16s had been promised to Israel "with the aim of reducing the overwhelming advantage in arms held by the Arab states."

The statement was devoid of recriminatory language, and Israeli sources said Prime Minister Menachem Begin's government wanted to avoid exacerbating the situation.

It has been an open secret for months that the president, who originally intended to give the required formal notice of the sale to Congress last June, has been holding the planes back while the United States seeks to achieve an agreement on withdrawal of Israeli, Syrian and Palestine Liberation Organization forces from Lebanon.

Until Thursday, however, the administration had refused to admit that fact publicly and had insisted that the matter was under consideration by Reagan. U.S. officials yesterday said privately that the president's decision to state his position openly appeared to have been prompted by frustration over what the administration regards as Israel's inflexibility in the Lebanon negotiations; and, while they acknowledged that Reagan clearly wanted to send a signal, he apparently acted in an impromptu manner.

Reagan's Los Angeles remarks are known to have caught Secretary of State George P. Shultz and his senior State Department aides by surprise. The president's move came as they were preparing for talks, which began yesterday, with Reagan's special Mideast envoy, Philip C. Habib, about what approach the United States should take now to break the Lebanon stalemate.

In what amounted to an after-the-fact reaction yesterday, the administration sought to present the president's move in a way that kept his message about the F16s intact while simultaneously signaling the Begin government that it should not be viewed as the first step in a campaign to use American military aid to put pressure on Israel.

In fact, Romberg said, it was a matter of record that the president notified Congress last summer that Israel's invasion of Lebanon might have put it in violation of the Arms Export Control Act.

When reporters said they had no recollection of such a notification being made, the spokesman replied that at the department's daily briefing last July 16--the day Shultz was sworn in as secretary--the then spokesman, Dean Fischer, said that a letter had been sent to Congress but refused to reveal its contents on the grounds that they were classified.

Romberg in Washington and Speakes in California both denied that there was any inconsistency in the refusal to go forward with the F16 sale after the administration last week approved the sale of Sidewinder air-to-air missiles for Israel.

Romberg said the "question of whether to apply the same reasoning to other weapons systems was a matter of judgment," and Speakes noted that the missiles, unlike the F16s, are "defensive weapons."

Romberg also said the F16 action was "not inconsistent" with Shultz's frequently stated position that the United States should not use aid to put pressure on Israel.

He implied that the F16 situation is essentially a matter of timing; when he was asked whether Israel will get the planes eventually, Romberg answered: "I think that's a fair statement." First deliveries of these 75 F16s are scheduled to begin in 1985.

Several major American Jewish organizations yesterday issued statements criticizing Reagan's action as unfair to Israel and calling on him to show greater patience in the drive for a Lebanon withdrawal accord.