The Saudi Arabian and Syrian foreign ministers presented President Reagan with a plan yesterday for temporarily evacuating trapped Palestine Liberation Organization fighters from west Beirut to northern Lebanon and sending the PLO political leadership out of the country, according to informed sources.

The plan, presented in a highly publicized visit to the White House by Saudi Arabian Foreign Minister Saud Faisal and Syrian Foreign Minister Abdal Halim Khaddam, is expected to generate a new round of diplomatic activity with Israel, the Lebanese government, other Arab nations and the PLO.

An administration official, without specifying details, told reporters in a briefing that the "new ideas" brought to Reagan by the two Arab League emissaries "add a new element of possible movement in the near future in the right direction."

The official also said the proposals "are going to form the basis of further discussions."

PLO Chairman Yasser Arafat proposed last Friday that his encircled troops be dispersed temporarily to other sites in Lebanon until a country of asylum can be found and that the Israeli siege of west Beirut be lifted.

The Israeli government is reported to have rejected a similar proposal in an earlier formulation.

To improve its chance of acceptance, the Reagan administration is reported to be urging the Arabs to come up with clear and definite commitments about where the PLO fighters will go after leaving northern Lebanon.

It is considered doubtful that Israel or the Lebanese government would accept transfer of the PLO military presence from Beirut to another part of Lebanon without receiving such commitments and understanding them as binding.

Evacuation of the PLO political leadership to another Arab country is thought to be more easily arranged. But the PLO leaders have been fearful that they could fall under the sway of the host government unless they have clear guarantees of their freedom of movement and expression.

After the White House meeting, Saudi Foreign Minister Saud told interviewers that he is "hopeful" of progress toward a political solution in Lebanon. But, like the administration official, he declined to specify proposals under discussion.

U.S. sources conceded that the proposal for an interim transfer of PLO guerrillas within Lebanon would present more complications than would the earlier idea of evacuating all of them to Syria in a first phase and later transferring many to several other Arab countries.

If the current plan works out, Syria, which balked at the original proposal, is considered likely to accept some of the guerrillas after they wait temporarily outside of Beirut.

This likelihood, which represents a change from the present Syrian public position, gave rise to reports yesterday that Syria has agreed to lift its ban on acceptance of the guerrillas.

With the discussions of the proposal here and in the Middle East at a very preliminary stage, sources here were guarded in any estimate of its chances for success. At the same time, it was clear that the main hopes for a peaceful resolution of the current crisis rest with the proposal.

While the plan was presented by the two ministers in their capacity as emissaries of the Arab League, it was unclear how many nations and groupings within the far-flung league are sponsoring the proposal.

In addition to the Beirut situation, the 80-minute White House meeting also touched on the broader issue of the rights and future status of the Palestinian people.

There was no indication from the official briefers or other sources of any change in the longstanding U.S. refusal to recognize or negotiate with the PLO until that organization accepts Israel's right to exist and two U.N. resolutions on the framework for Middle East peace.

In a meeting early yesterday with the House Foreign Affairs Committee, Secretary of State George P. Shultz restated his determination to deal with the underlying Palestinian issue, according to a participant.

Shultz reportedly gave no details on how he would tackle the problem, though, and said he saw no need to change the U.S. terms for dealing with the PLO.

Despite a flurry of reports, to which he referred as "a lot of rumors," the administration official who briefed reporters said no definitive word has been received from the PLO about a shift toward accepting the U.S. conditions.

White House officials said there was no discussion in the meeting of possible Arab retaliation against the United States if Israel attacks west Beirut using U.S.-supplied weapons. Such a possibility had been raised Monday by Senate Foreign Relations Committee Chairman Charles H. Percy (R-Ill.) after a meeting with Saud.

Saud also said that possible retaliation had not been discussed in the White House meeting and that such a question is not one to be dealt with, especially in the environment of the White House.

"I think we were able to convey to the president the seriousness and the willingness and the decision of the Arab countries to bear their responsibility," Saud said.

"The issue from our point of view is the issue of the independence and territorial integrity of Lebanon. The primary concern is the withdrawal of the aggressor, Israel," he said.