Egyptian President Anwar Sadat, touring Europe to win support for his Middle East policies, is to have a private meeting in Salzburg, Austria, today with Shimon Peres, leader of the opposition Labor Party in Israel.

Austrian Chancellor Bruno Kreisky announced yesterday that he arranged the unexpected meeting to give Sadat an opportunity to hear directly the views of Israel's main opposition party, which had governed Israel for nearly 30 years until its election defeat last May.

Observers in Jerusalem said it was unlikely that Peres, in his meeting with Sadat, would adopt positions or express views that would significantly challenge the negotiating policies of Israeli Prime Minister Menachem Begin and his Likud coalition.

The meeting could take on political significance in Israel, however, observers said, because it could indicate that Begin realizes that, with peace negotiations bogging down, he needs the Labor Party as a partner in his bargaining with Egypt.

While relations between Peres and Begin had been strained for many months after last year's elections, in recent weeks they appear to have improved markedly. The two had a long meeting before Peres left for Europe earlier this week.

Sadat had been scheduled to meet only with Kreisky during a brief stopover in Salzburg today and Peres, Israel's former defense minister, was to be traveling from West Germany to Vienna for a Socialist International meeting on the Middle East Sunday.

When he proposed to the two that they meet, Kreisky said in an interview on Austrian television, both showed "a certain willingness to establish contact."

It was unclear yesterday whether the talks would be substantive or merely ceremonial, but in any case a meeting between an Egyptian president and an Israeli opposition leader could be expected to improve the atmosphere of the negotiations, observers here said.

Sadat met with a Labor Party group headed by Peres when he was in Jerusalem last year, but the two had no opportunity then for private talks.

Begin is scheduled to meet today with the U.S. ambassador to Israel, Samuel Lewis, for a briefing on talks last weekend between Sadat and President Carter at Camp David.

Begin returned to Israel yesterday from a fund-raising visit to Switzerland. He said that the peace negotiations would be discussed Sunday when the Cabinet holds its regular weekly meeting.

Begin also denied published reports that he had presented to Sadat's differenc peace plan than he had told President Carter he would be presenting.

The Israeli daily Maariv reported this week that Carter, in private meetings with congressional and American Jewish leaders, has complained that the proposal Begin gave Sadat at Ismailia, Egypt, in December differed substantially from a Begin plan that Carter had blessed in advance as a fair basis for negotiating.

According to Maariv, Carter had suggested to visitors that these discrepancies brought Begin's credibility into question. The paper said Begin has begun compiling documents to refute the allegation and to provide a full explanation for Carter.

Meanwhile Secretary of State Cyrus Vance in his news conference yesterday, denied an Israeli press report that Washington is trying to arrange another summit meeting between Sadat and Begin.

Vance added, however: "We're totally flexible Anything to move the process forward we would consider. At the moment, though, it doesn't seem necessary."

In New York yesterday, Israeli Foreign Minister Moshe Dayan said he was told by U.S. Assistant Secretary of State Alfred Atnerton on Thursday that Middle East peace talks, which broke off last month, would resume "sometime after next week."

State Department sources said, however, that the resumption probably would not come that soon because Egypt and Israel still have not agreed on a declaration of principles that would be the basis for the talks.

Atherton is to begin a shuttle visit to the Middle East later this month in an effort to get the two countries to agree on a declaration of principles.