The Palestine Liberation Organization, in a seathing statement released here today, rejected U.S. mediation efforts in the Middle East and reaffirmed its opposition to U.N. Security Council guidelines for a peace settlement.

The action by the Central Council, the PLO's 55-member policy-recommending body, appeared to end for now any hopes that a softened attitude on the part of the most influential Palestinian organization might aid peace-seeking efforts.

The possibility that the PLO might revise its long-held positions on key issues had been raised during Secretary of State Cyrus Vance's recent peace mission to the Middle East, but the hardline stance of Israeli Prime Minister Menahem Begin apparently made the PLO unwilling to make concessions.

PLO sources also accused the United States today of refusing to make meaningful concessions in its own rigid policy toward the PLO.

[A State Department spokesman said in Washington that he did not expect a formal U.S. government reaction to the PLO communique. Vance was returning from a visit to China and was unavailable for comment.]

At the time of Vance's mission, President Carter had said that the United States might open a dialogue with the PLO if the PLO accepted U.N. Security Council Resolution 242. That resolution, adopted in 1967, contains a formula for a peaceful settlement in the Middle East but makes remention of a Palestinian nation, refering only to the need for a solution to the "refugee problem."

Sources here said the PLO had been willing to accept Resolution 242 - but only if Israel recognized the Palestinian right to a homeland and the resolution were reworded to that effect.

The entire initiative collapsed when the United States refused to concede anything beyond its promise to talk to the PLO, the sources said.

The cornerstone of PLO policy has been the effort to gain universal recognition of the Palestinians' right to a state of their own.

"Despite all our efforts to get the United States to give us some assurance that this would happen if we recognized Israel, they adamantly refused," one of the leading Palestinians at the council meeting said.

The Central Council is a liaison body between the Palestine National Council and the PLO executive committee, the 15-man "cabinet" headed by Yasser Arafat. It has no power to make binding policy decision, but its composition is representative of the National Council and its recommendations have major impact on the National Council's decisions.

Council speaker Khaled Fahoum said after today's meeting that the Central Council's next meeting would be in September, after Arafat returns from a visit to Moscow scheduled to begin next week.

Aster a stormy overnight meeting and a three-hour afternoon session, the Central Council issued the communique, condemning "Zionist and United States imperialist plots to liquidate the Palestinian cause."

The statement said in effect that the United States is as much a villain as Israel in the Middle East situation and accused it of ignoring "the rights of the Palestinian people."

There was no official Israeli comment, but an Israel government official said privately that, for this country, it "removed a potential point of argument with the United States."

Privately, some Israeli officials admitted that any major PLO compromise on its terms for entering peace talks could have been awkward for Israel. Israeli leaders have shown themselves increasingly irritated at international attempts to coax the PLO into negotiations.

Despite the recent U.S. efforts to reach an accomodation with the PLO. Begin has refused to consider dealing with the organization.

The PLO communique also called on Arab governments "to beware of believing American and Zionist promises and to face up to these plots" against the Palestinians.

The Palestinian sources said the PLO's newly enunciated attitude toward the United States has the full backing of Syrian President Hafez Asad, a pivotal figure in any Middle East peace talks.

This was reflected in editorials in Syria's government-controlled press this week charging President Carter with being "brainwashed" by Begin. The editorials said U.S. failure to protest more vigorously Begin's policy of extending Israel's hold on the occupied West Bank of the Jordan River means that Washington "is no longer capable of fulfilling its role as an impartial mediator."

Political analysts here said there are signs that Egypt, Jordan and Saudi Arabia are also becoming disenchanted because of the absence of stronger U.S. reaction, to Begin's actions.