President Carter and Egyptian President Anwar Sadat yesterday concluded their discussion of ways to break the impasse over Palestinian self-rule, but said no decisions can be made until Carter had similar talks with Israeli Prime Minister Menachem Begin here next week.

Appearing with Sadat in the White House rose garden, Carter characterized their two-day meeting grandly, calling it "perhaps the most far-reaching discussion in my experience as president," and said he had kept Begin informed about the main points.

Carter added that he would give "a full report" to Begin before the Israeli leader arrives Tuesday for the second stage of the meetings aimed at finding a self-government system for the Palestinian inhabitants of the Israeli-occupied West Bank and Gaza Strip.

Sadat said, "We have discussed and explored all possible alternatives to give momentum to the peace process." Recalling how Carter moved into the breach 13 months ago to fly to the Middle East on a mission that resulted in the Egyptian-Israeli peace treaty, Sadat added:

"At this moment, there are lots of difficulties and new divisions in our areas . . . But with the help of the people of the United States and with the help of President Carter, I'm sure we can reach agreement and overcome the difficulties."

He cited the new turmoil stirred in the Middle East and Southwest Asia by the crises in Iran and Afghanistan as making even more urgent the need to defuse Arab-Israeli tensions through an agreement on Palestinian autonomy.

In an interview with ABC television last night, Sadat said, "I'm ready to give the United States every facility to reach the Persian Gulf" should the states of the region be threatened by the Soviet Union.He did not elaborate, although in the past he has offered the use of Egyptian base facilities for refueling and servicing U.S. planes while stopping short of offering permanent bases.

At a White House dinner Tuesday night, the two leaders made clear that they no longer have much hope of concluding the autonomy agreement by its May 26 target date.

However, the Egyptians, with the general concurrence of the United States, are hopeful that Carter's separate talks with Begin and Sadat will pave the way for a new round of extended negotiations here later this month.

Under this tentative plan, the top negotiators from the three countries -- U.S. special ambassador Sol. M. Linowitz, Egyptian Prime Minister Mustafa Khalil and Israeli Interior Minister Yosef Burg -- would be given increased flexibility to try and bring an accord close to completion in on last burst of intensified effort.

However, reliable sources said yesterday, the Israelis still must agree to cooperate in following that course; and, the sources added, whether Israel is willing won't become clear until Carter talks with Begin.

In addition, any new negotiating round would depend on whether Carter can find some mutually acceptable compromises that will give hope of resolving the disagreements that have stalled the autonomy talks for 10 months.

Although several highly technical disputes are involved, they all stem from the continuing wide gap between Egypt's demand that the West Bank and Gaza Palestinians be given broad self-governing rights, making them virtually autonomous from Israel, and Israeli insistence on limiting any self-governing authority's powers so severely that it could not become the nucleus of an independent Palestinian state.

At his Tuesday dinner for Sadat, Carter, in making what he called "a toast to peace," seemed to be coming down on the Egyptian side of the argument. He recalled that the 1978 Camp David accords agreed to by Begin and Sadat specify "the organization of a self-governing authority in the West Bank and Gaza derived through free elections held by the people who live in those two troubled areas."

Carter said Israel "has agreed to withdraw the military government and civilian administration associated with it and then to withdraw all her troops from the occupied territories with the remainder of those troops to be located in specified security areas."

Then, in what many diplomatic observers singled out as the key part of his dinner toast, Carter said: "The people of those two territories are granted autonomy, and as Prime Minister Begin said many times in the presence of President Sadat and me, not just autonomy -- full autonomy. 'Full autonomy,' he said many, many times."