audi Arabia and Egypt have overcome three years of estrangement to work in tandem to press the United States to use its influence with Israel to bring the Palestinians into a rejuvenated Middle East peace process, according to well-informed Palestinian officials.

The timing of the Israeli invasion three weeks ago caught the Arab world at the height of another of its recurring periods of disarray. For the first several days, the response was tepid at best from the many states that have declared themselves the enemies of Israel and the protectors of the Palestinians.

With no military help from the radical Arab regimes that have traditionally supported them--except for Syrian troops, the other target of the Israeli invasion--the Palestinians find themselves now depending on two of the conservative Arab states with which they have been fundamentally at odds in recent years.

Egypt and Saudi Arabia--Washington's closest Arab allies--have cooperated closely despite their lack of diplomatic relations to make clear to the Reagan administration the cost to the United States and all moderate Arab regimes of an Israeli assault on West Beirut.

Starting roughly two weeks ago when Egypt and Saudi Arabia reportedly sent a stiff joint message to the United States, the two governments have pleasantly surprised the Palestinians, who have been angered that other Arab states abandoned them during their ordeal.

The PLO's newfound benevolence toward Egypt--which it considered a traitor before the invasion for signing a separate peace treaty with Israel, freeing the Israeli Army to attack the guerrillas--is symptomatic of a major change of heart.

Egyptian Deputy Foreign Minister Butros Ghali has met at least four times with PLO representatives during the past 10 days.

Egypt has cooperated by sending an Egyptian-based brigade of the Palestine Liberation Army to Lebanon since the invasion, according to Palestinian officials.

In a letter this week to leaders of the European Community, Egyptian President Hosni Mubarak uncharacteristically criticized the United States for its response to the invasion, accusing it of a "lack of firmness" that "gives Israel the impression that it can count on an American backing regardless of its policy toward the Palestinian people."

The Palestinians are well aware of Mubarak's self-interested motives in winning his way back into Arab circles, but are politic enough to express their "surprise and delight" with his support.

Palestinians, even radicals who once threatened to overthrow the Saudi monarchy, also are singing the praises of King Fahd.

"We are lucky to have him as a friend," one Palestinian official said. "He has been very faithful."

Both the Egyptians and the Saudis, Palestinian officials said, have told the PLO, meanwhile, that the White House is "working on" some new form of self-determination for the Palestinians.

The clear intimation is that this would go beyond the narrow limits imposed by Israel on the stalled autonomy talks for the occupied West Bank and Gaza Strip.

Judging from comments by Palestinian officials, the PLO, once violently opposed to such talks, is now interested in such new initiatives.

One high Palestinian official maintained that the Egyptian government thought it "possible" that within "the next few weeks" there would be a meeting of Palestinians, Egyptians and Americans.

Palestinian officials point out now that with a weakened Syria no longer in a position to dictate to the PLO, the Palestinians could accept the Middle East peace proposals offered by Fahd last year.

That plan, which was thwarted by Syrian opposition, implicitly recognized Israel's right to existence by approving two key U.N. Security Council resolutions containing language to that effect.

While the Fahd plan has been emphatically rejected by Israel, it nonetheless marks an important shift in Arab thinking about the Jewish state.

Although it brought Egypt and Saudi Arabia closer together, the Israeli invasion has had no similar effect on the rest of the dissension-ridden Arab world. Early in the invasion, the PLO first asked where its Arab friends were and then when there was no response, bitterly complained about the lack of help. When Syria agreed to a cease-fire with Israel, a PLO official accused it of having "plunged a knife in the back of Palestinian and progressive Lebanese forces" and there were anti-Syrian demonstrations in Palestinian refugee camps around Damascus.

Although Syria is considered by many observers to be a likely recipient of the PLO guerrillas if they leave West Beirut, relations between PLO leader Yasser Arafat and the Syrian government of President Hafez Assad are poor, according to Western diplomats and other sources in Damascus.

"There have been strains and difficulties between Arafat and the Syrians," said a senior European diplomat in Damascus with long experience in the Middle East.

The radical Libyan regime of Col. Muammar Qaddafi, regularly one of the most vocal backers of the Palestinians, has issued daily declarations of solidarity with the PLO but has done little else. It boycotted a meeting last week of Arab League foreign ministers, calling it a "degradation" of the Arab people and part of "the great conspiracy against the Palestinian cause"--on the grounds that the meeting should have been at summit level and earlier.

Bassam Shaka, a Palestinian deposed by Israel last year as mayor of Nablus on the occupied West Bank, strongly attacked Arab states for their inaction, according to a statement published by Wafa, the Palestinian news agency, today. Shaka said "most of these regimes' policies are in complete harmony with Washington's, as was clear in the lack of reaction to the Israeli massacre of the Lebanese and Palestinian people."

Egypt held itself out of an active diplomatic role in the negotiations for several days, reportedly through initial confusion resulting from its underestimation of how far Israel would go in Lebanon.