Israel Defense Minister Ezer Weizman flew to Salzburg, Austria, yesterday for a surprise meeting with Egyptian President Anwar Sadat in which the two discussed ways of reviving the stalemated Middle East peace negotiations.

Sadat and Weizman met for more than three hours, and the Israeli Defense Minister subsequently termed their discussion "very useful."

Weizman said he had brought with him new proposals for breaking the deadlock between the two countries, but he declined to discuss the proposals with reporters.

"You will understand that my first report has to go to Prime Minister [Menachem] Begin," Weizman said. "I cannot reveal any details beyond stating that I have enjoyed the talks, and I think they were useful." He added, "I'm most encouraged."

The discussions were said to have been wide-ranging and not limited to military and security matters that Weizman previously had discussed with Egyptian officials in Cairo.

One topic reportedly discussed was a peace formula developed by the Socialist International in Vienna last week following a meeting between Sadat and Israeli Labor Party leader Shimon Peres.

Weizman also said at the conclusion of yesterday's talks that he and Sadat had agreed to continue their discussion in Alexandria, Egypt, at a date not yet decided.

The unexpected Weizman-Sadat meeting came as even more of a surprise as it took place only five days before next Tuesday's scheduled meeting in London of Israeli Foreign Minister Moshe Dayan, Egyptian Foreign Minister Mohammed Kamel, and Secretary of State Cyrus Vance.

Yesterday's meeting thus raised hopes that the stalemate that has prevailed in the Egyptian-Israeli peace talks since last January has been broken.

Weizman's visit with Sadat, their first since March 31, also came amidst reports that the two countries will continue talks after the London meeting at El Arish, a town in the Israeli-occupied northern Sinai.

The only official Israeli comment, on this possibility came yesterday from Dayan, who told a news conference: "We are ready for talks at El Arish but I cannot confirm that this has been agreed between the parties."

Weizman and Sadat met yesterday in Fuschl Palace, a 15th century lakeside estate outside Salzburg, where Sadat has been vacationing since Monday.

The meeting was in response to an urgent message to Weizman Wednesday from his Egyptian counterpart, War Minister Mohammed Ghani Gamassi.

The inultation came as a particularly surprise to Israelis because that very day, Gamassi had been quoted in Cairo as saying that meetings between the Egyptian and Israeli generals were unwarranted "as long as there is nothing new to discuss."

Gamassi's invitation, according to Israeli government sources, was discussed Wednesday night by Prime Minister Begin and several ministers, including Foreign Minister Dayan.

Dayan was said to have at first opposed the meeting as a ploy by Sadat to further divide the Israeli cabinet over the peace issue, but that Begin decided Weitzman should resume direct contact with the Egyptians.

After the late-night meeting Weizman flew to Salzburg early yesterday morning in Israeli-made Westwind executive jet. He was accompanied by maj. Gen. Abraham Tamir, head of the Israeli army's long-range security planning section.

Weizman first met briefly with Gamassi, after which Gamassi conferred with Sadat, presumably informing him of the message Weizman brought.

Then as Gamassi and Egyptian Foreign Minister Kamel sipped coffee on a terrace, Sadat and Weizman talked privately for more than three hours.

Following their discussions, Weizman was reported planning to dine with Gamassi before flying back to report to Begin.

Some Israeli officials last night interpreted the Sadat-Weizman conference, coupled with the upcoming London foreign ministers meeting, as a victory for Begin since Egypt had insisted it would not renew discussions until Israel brought forward singificant new concessions that, in Israeli's view, represent "prior conditions."

Weizman was reported to have taken no territorial concessions to Salzburg, although government officials would not discuss what the defense minister's instructions were or

Israel officials also pointedly noted in contrast to next week's London conference, was arranged without any diplomatif pressure from the United States.

Israeli sources said, however, that both sides gave advance notice of the Salzburg meeting to the Americans.

During his press conference yesterday Dayan said that although Egypt and Israel are still far apart in the peace process, he sees some possible "meeting points" in the two countries' peace plans.

"We have to look at all kinds of avenues to see if these points . . . can serve as a basis for progress and advancement," Dayan said, in a remark that seemed to contradict his ministry's recent condemnations of the Egyptian peace plan as "totally unacceptable."

Government sources said Dayan was becoming increasingly sensitive about published insinuations that recently almost everybody in Israel except the foreign minister has been conducting peace talks with Sadat.

However, Dayan insisted yesterday that he was "very glad" Weizman was talking with Sadat.

"I would very much like to hear Mr. Weizman when he comes back on his impressions of what he discussed with President Sadat," Dayan said.

The two men for years have been rivals for the limelight in Israeli politics. Their conflicting personalities and political views have frequently surfaced publicly, most recently during the drafting of Israel's response to the Carter administration's queries about the future of the West Bank and the Gaza Strip.