Israeli Prime Minister Menahem Begin returned today from his talks in Egypt to find mounting domestic opposition to the deal he has offered the Egyptians.

A cheerful Begin stepped off the plane, saying he has appealed to the people of Israel before he departed for the summit "to pray for our success. If indeed our people did pray, their prayers were heard."

But during a press conference in which he and his two key aides - Foreign Minister Moshe Dayan and Defense Minister Ezer Weizman - answered questions about the Ismailia talks it became apparent that the assessments of the three men differed on some key issues.

While Begin told his countrymen that the meeting was "crowned with success" Dayan spoke of the "wide gap" between Israel and Egypt, and Weizman said. "We are not on easy waters."

Apparently in preparation for a major foreigh policy debate scheduled in the Israeli parliment Wednesday, Labor Party opposition leader Shimon Perces said that Begin had gone too far and given away too much by way of proposed concessions to the Egyptians in the Israeli-occupied Sinai peninsula.

Because of the great buildup by Begin and Egyptian President Anwar Sadat of expections off a major breakthrough toward peace, disappointment that it had not come about seemed palpable in Israel today.

One pro-Begin member of the Democratic Movement for Change, the left wrong of the conservative ruling coalition, said that today's decision to refer the main Arab-Israeli dispute to months of committee work means that Begin may have lost his chance to prevent formation of a powerful opposition to the concessions he has offered Egypt in exchange for peace.

Begin's ability to head off such opposition, in the view of this deputy, depended on moving so fast that his political opponents could not organize, especially in Begin's own Likud group, with its ideological commitment to keeping all of the occupied biblical lands.

Begin seemed today to be gearing up for Wednesday's debate, saying that the new "personal accord" he has found with Sadat is a "great joy and consolation for the many years in which some people used to say that if we took office the following day there will be war."

Peres indicated to reporters that his criticism of the Sinai proposals signaled a change in tactics. He made it clear that his Labor Party, the government's main oppposition on the left, would stop stressing the theme that Begin is selling out the Israeli settlers in the occupied Arab lands. That identified Labor too much with Begin's right-wing opposition, Peres indicated.

Instead, the Labor leader said he would attack Begin as a poor tactician because he offered major concessions in the Sinai hoping that Sadat would respond with coneccessions [WORD ILLEGIBLE] the occupied West Bank of the Jordan. Sadat apparently did not [WORD ILLEGIBLE] from his view that the West Bank should get independent statehood.

In Peres' view, the Egyptian leader has simply pocketed for the future what Begin offered him [WORD ILLEGIBLE] Sinai.

Dayan said that disagreements over the Sinai are as wide and serious as those over the West Bank, the only issue that Begin and Sadat highlighted today as a source of discord.

Slightly more optimistic that Dayan, Weizman called the Sinai a "side issue," but said that Israel is "not on easy waters there either." Weizman who is to be the co-chairman of the military committee that will meet in Cairo to deal with the Sinai, told reporters not to ask too many questions about it since it is so delicate.

Dayan said he was "pleased" with the Ismailia meeting only because both sides agreed to keep talking despite their differences. He said Egypt must now make "painful concessions" in Sinai or not get any agreement at all.

On the West Bank, Begin refused to give any details of his proposals to Egypt, saying that he wants to announce them first in Parliament Wednesday.

He said progress has been made on that problem, because "we suggested self-rule - it's a great event in the history of this country and of the Palestinian Arabs."

Asked how to explain "how a people can be given self'rule and not be allowed to choose their own form of government, state and constitution," Begin merely replied, "This is a philosophical question."

Reporters here detected signs of personal tension between Begin and Dayan. There was a noticeable contrast in the way Begin referred to Weizman and to Dayan, both of whom were sitting at a table next to the lectern where Begin gave his press conference at Ben Gurion airport.

THe prime minister spoke fo Weizman as a man "whom the Egyptians respect as a courageous soldier." But Begin spoke of Dayan, a former general with a far wider military reputation, only as "the foreign minister," without using his name. Dayan rose from the table and walked from the press conference, leaving Weizman sitting alone.

By dividing the negotiations into two parts, under a political committee and a miliary committee, Begin has in effect made Weizman Dayan's equal.

When Dayan agreed to defy his own Labor Party to become Begin's foreign minister, it was widely assumed that Dayan had been appointed as the heir apparent to Begin, a man with a serious heart condition. But Begin has turned incresdingly openly to replace Dayan with Weizman in that role.

Begin's opponents inside his own Likud bloc are becoming increasingly restive. The chairman of the Whole Land of Israel Movement, a militant religious pro-settlement organization in the Likud, resigned in protest from the bloc's executive body.

Reports of the emotion-charged debate Begin participated in Friday in Likud caucus are beginning to leak to the press.

"I have devoted my whole life to the struggle for the Land of Israel," Begin reportedly said, "and I do not need a certificate showing that I am 'kosher' from any of the religioua settler groups.

In a preview of Wednesday's debate, a routine measure extending the government's emergency powers in the occupied territories was turned into a parliamentary shouting match of several hours duration today.