Despite his bitterness over what he regards as a U.S. betrayal of assurances to protect Palestinian civilians in camps near Beirut, Palestine Liberation Organization Chairman Yasser Arafat says he has not closed the door on future cooperation with the United States to achieve a comprehensive Middle East peace.

In an interview Wednesday with The Washington Post at his new headquarters here in a rundown beach hotel 25 miles south of Tunis, Arafat explained that he was resigned to dealing with the United States as the dominant superpower in the region. "I am pragmatic," he said. "I have to deal with facts and realities and not dreams."

The bearded PLO leader even praised some aspects of President Reagan's Middle East peace plan, enunciated Sept. 1, despite the criticism it has evoked among some other PLO officials.

"There are some positive elements in this," Arafat said, sitting at a big desk with a Palestinian flag planted behind him. "For the first time Reagan has begun to say that Gaza and the West Bank are occupied areas and not for annexation or settlements."

Arafat insisted that his recent meetings in Jordan with King Hussein about the possibility of some future confederation between an independent Palestine on the West Bank and Gaza and the Kingdom of Jordan on the East Bank, in no way implied that he was delegating the PLO's designated role as the "sole legitimate representative of the Palestinian people" to the Jordanian monarch.

Reagan is understood to have asked Arab leaders who visited him in Washington last month to urge the PLO to delegate the job of negotiating with Israel over the occupied territories to King Hussein in view of Israel's refusal to recognize or consider bargaining with the PLO and the PLO's refusal to recognize Israel or U.N. Security Council resolutions 242 and 338.

Arafat contended that Hussein had never asked him to divest himself of the PLO authority and that no one else had made such a suggestion to the PLO.

Despite his conciliatory comments about working with the United States in the future, Arafat adamantly maintained that the United States must share some of the blame for last September's massacre of hundreds of Palestinian civilians by Phalangist militiamen.

The PLO chairman and his aides claimed that special envoy Philip Habib had repeatedly passed on to the PLO written "guarantees" promising the Palestinians adequate security in his efforts to convince the PLO to evacuate its forces from besieged Beirut where they had been trapped by Israel's invasion of Lebanon June 6.

The U.S. failure to stand by the official commitments it made, Arafat said, had severely damaged U.S. credibility and honor in the area. He said it also raised large doubts about the value of future commitments by Washington that might be made to assure a genuine Middle East peace.

"We put our trust in the United States as a superpower to keep its word," Arafat said. "But what happened is shameful."

Prior to the interview, one of Arafat's chief lieutenants provided the Post with key documents from last summer's indirect negotiations between Habib and the PLO to back up the organization's claims of betrayal by Washington. The negotiations resulted in an agreement Aug. 18 for the evacuation of the PLO leadership, staff, and military forces from West Beirut where they had maintained their capital in exile for the past decade.

The documents show that in at least three instances the United States undertook not only to guarantee the safe departure of PLO forces but also the "security of the camps" where Palestinian civilians lived south of the capital.

The United States made such assurances, however, only on the basis of verbal promises from the Israeli government and the Phalangist militia leader, Bashir Gemayel, who later was assassinated before he could assume elected office as Lebanon's president.

State Department officials conceded in Washington that the United States accepted only oral commitments from Israel and the Phalangists regarding the safety of the camps.

"We felt there was no question that Bashir could control his militia," explained an official. "We trusted him since he had honored previous promises, but circumstances changed when he was assassinated."

"As far as the Israelis were concerned, we realized that anything written down would have taken forever to get accepted."

It was the lack of a written agreement that Western diplomats claim left the United States diplomatically naked when Israel chose to ignore the verbal understanding it had made with Habib and invade Beirut on a pretext of imposing order after Gemayel's assassination and rooting out an alleged 2,000 PLO fighters that Israel claimed, but never documented, had refused to leave the capital.

Arafat and other PLO officials said they accepted the Habib agreement because they thought the United States would not make promises it could not keep.

Another factor, according to PLO Foreign Minister Farouk Khadoumi, was that when the series of U.S. commitments was made in early August, the Israelis had intensified their air, sea and artillery bombardments of West Beirut to such an unprecedented scale that the mounting destruction and casualties, civilian as well as military, prevented the PLO from quibbling about details.

"I don't think we made a mistake; we had no other options except to accept the guarantees given," Khadoumi said in a separate interview here. "We never thought a superpower would not respect its guarantees."

Despite all their martial swagger and boast that their goal was the liberation of Palestine, the role of the PLO fighters in fact was always more that of protecting the half million Palestinian refugees in Lebanon than providing a serious military threat to Israel's superior forces.

On Aug. 3, exactly a month after it had signed a paper committing itself to leaving Beirut, the PLO sent Habib a five-page document in Arabic with 11 specific points regarding an eventual agreement to evacuate.

Significantly, the first point asked for a cease-fire in place that would allow a disengagement of forces around Beirut and the interposition between them of a multinational military force that would prevent Israel, or its anti-Palestinian Christian allies, from taking advantage of the PLO abandonment of its positions.

The second point in the document was a specific demand for security guarantees for the withdrawing Palestinian military forces and "guarantees for the safety of the Palestinian camps from any aggressions."

The United States reply sent to Arafat through Prime Minister Shafiq Wazzan read: "Regarding the U.S. government guarantees as regards security for the departing Palestinian forces along with the security of the camps. Comment: We will provide these guarantees."

In at least two other similar communications in the next couple of days the Habib delegation restated that point. On Aug. 4, replying to another note from the PLO, the United States specified in point 10 of a 14-point paper that "we appear to be in agreement on the Security Council resolutions and on U.S. assurances about the safety of the departing Palestinians and the camps."

Two days later, on Aug. 6, another four-page U.S. note was passed on to the PLO listing 11 "points of agreement." The eighth of these cited: "U.S. guarantees governing the safe passage of the departing Palestinian forces as well as the Palestinian camps."

That sort of language was missing from the published Aug. 18 agreement because it would have required the protracted Israeli scrutiny that Habib feared would bog down the momentum of the talks. Instead of the earlier language given to the PLO, the published Aug. 18 accord spoke only of the three-nation multinational force (American, French, Italian) helping the Lebanese Army to assure the "safety of departing PLO personnel" and to assure "the safety of other persons in the Beirut area."

That language was even too vague for Prime Minister Wazzan who demanded it be made more specific. Habib sent an amendment to the prime minister in which he reiterated the "importance" the U.S. government attached to Israeli guarantees to honor the accord, including the security of "other persons in Beirut" -- a veiled reference to the Palestinians.

Habib told Wazzan in the letter, which then was passed on to the PLO, that the U.S. government would "do its utmost to insure that those Israeli assurances are scrupulously observed."

Arafat said that there were dozens of other issues beyond the specific U.S. guarantees on the camps that were not in the Aug. 18 document but which were part of the final deal, having been worked out in separate addendums or letters outside the scope of the final document.

These included not only the circumstances and details of his own evacuation and departure and the deployment of the multinational forces, but also U.S. assurances that it would pursue with the Israelis the "fate and treatment" of Lebanese and Palestinian prisoners held by the Israeli Army in southern Lebanon.

Arafat considers this latter U.S. commitment to pursue the issue of the prisoners the only U.S. pledge Washington has honored. "Truly they have kept their word on this point," Arafat said, pointing out that to date U.S. efforts have resulted in the release of what he estimated to be some 3,000 Palestinians and another 2,000 Lebanese.

Arafat pointed out that like the earlier guarantees about the security of the camps, the U.S. assurances to work on the prisoner issue also were not a part of the final published Aug. 18 accord.