Prime Minister Menachem Begin said today that the Middle East peace negotiations are at a "very delicate" juncture and that President Carter must persuade Egyptian President Anwar Sadat to accept compromise proposals that Israel has already approved.

Amid growing indications that the Israeli Cabinet will resist any substantial changes to the compromise draft it approved by a narrow margin on Monday, Begin returned here to assuage fears in his government that Israel faxes another round of demands for concessions.

"Israel awaits a positive replay from Egypt," Begin told reporters on his arrival at Ben-Gurion Airport.

The prime minister sounded a generally positive note in his remarks, however, speaking of signing a treaty not during Carter's visit to Jerusalem, but in "a week or two."

He also did not rule out the possibility of another round of three-eay summit negotiations to resolve lingering differences between Israel and Egypt.

Begin characterized his visit to Washington as an unqualified success, saying that if the peace proposals had remained as they stood when he got there, he would have left the U.S. capital with "a resounding no." But instead, Begin said, he returned with proposals that "the whole nation can accept with a clear conscience and a quiet heart."

He said he will brief the Cabinet Friday on the proposals and also brief the parliament's foreign affairs and defense committee, providing the committee promises secrecy. He said it is a matter of "life and death" that details do not leak from the committee.

Deputy Prime Minister Yigael Yadin has refused to brief the parliamentary committee, long the source of leaks of sensitive foreign policy information. In pique over that refusal, the committee refused to hold any meetings until it has been informed about Begin's trip.

Much of the substance of the compromise agreements, however, already has been published here and abroad.

When asked about reports that he and Carter had discussed a U.S.-Israeli defense pact, Begin said such an arrangement should be initiated by the Americans, but that if it is offered, he would recommend its acceptance.

It was clear that Begin already faces formidable opposition in his own Likud coalition to any substantial changes to the compromises reached in Washington. The Central Committee of the National Religious Party, a pivotal element in the coalition, instructed its three Cabinet ministers not to approve any changes without authorization from the party leadership.

Moreover, the full parliament, or Knesset, will have to approve that treaty, and rightist members the Likud bloc already are beginning to voice opposition to the compromises, much less any agreement with still more concessions.

Begin did not say what he himself will do if Egypt demands changes in the treaty proposals, telling reporters only that he would "read them."

The opposition Labor alignment, which swung the balance in favor of the original Camp David agreements, remains torn between support of a peace treaty with Egypt and opposition to the autonomy plan for the West Bank, which it fears inevitably will lead to a Palestinian state.