Israeli Prime Minister Menahem Begin has disclosed that Israel and Egypt seek a comprehensive understanding in the Middle East that other Arab states will then be invited to endorse.

This was reported tonight by British sources present at talks between the Israeli leader and Prime Minister James Callaghan.

Officials in Begin's party emphasized that Israel and Egypt are not seeking a separate peace treaty between themselves, but these Israeli sources would not quarrel with the British description of the direction of the talks between Cairo and Jerusalem.

At the same time, the U.S. State Department said that Under Secretary of State Philip Habib had spent yesterday here and then had left today for Moscow. Sources here said that Habib made no contact with Begin or his party which arrived in London on Friday. The trip to Moscow by Washington's top Middle East official was regarded here as further evidence of the far-reaching goals of the new Israeli-Egyptian dialogue.

The disclosure here gives the first clear picture of the ambitious nature of the Israel-Egypt talks. It now appears that the two states seek nothing less than a broad agreement to guide a peace deal in the Middle East, which would be followed by separate negotiations between Israel and each Arab state over details that concern it.

Washington Post correspondent Thomas W. Lippman reported from Cairo yesterday that President Anwar Sadat is describing his talks with Israel in much the same terms, Sadat was said to want an agreement in principle with Israel that he could then present to the other Arabs. If they endorsed it, Syria would then bargain with Israel over the Golan Heights, Egypt over the Sinai and others over the nature of a Palestinian entity.

Sadat reportedly hopes for Israel's agreement to give up territories won in the 1967 war and to accept some Palestinian entity in return for recognition and peace. This would free Sadat to work out the details of Egypt's special claims without waiting for all the others.

Begin is known to be distressed at the lukewarm support that the European Common Market, which includes Britain, has given to his talks with Sadat. According to officials here, he was careful in his meeting with Callaghan today to avoid any suggestion of a rebuke, but he was said to have stressed that a process toward peace is under way, that there should be no interference and that the dialogue should be encouraged.

British sources said that Callaghan agreed that the talks are a step toward peace and should continue - a move positive assessment than Britain or its eight Common Market partners have made so far.

Until now, the British quietly and the French more openly have limited themselves to praising Sadat's "courageous initiative" but expressed fears that it would jeopardize the comprehensive settlement needed for peace in the Middle East.

The British view has been that a comprehensive settlement depended on unity among the Arabs and that Sadat's bold move has split them. Both the British and the French have been particularly sensitive to Arab opinion since the price of oil was quadrupled four years ago.

British officials made it clear that Callaghan still believes that Middle East peace depends on the agreement of all the Arab interests involved. Nevertheless, there is now less disposition in London to think that the bilateral Israeli-Egyptian talks are an obstacle to this end.

In effect, Begin's theme here has been: "Don't kibbitz; applaud and encourage," Callaghan appears to have replied, "Let's give your two-sided talks a chance."

In Moscow today, Pravda, the Communist Party paper, said that Cairo's planned meeting with Israel and the United States on Dec. 14 "has seriously complicated the situation in the Middle East."

The proposed gathering, said the Soviets "has the proclaimed aim of preparing but the actual purpose of undermining the Geneva conference."

The Soviet Union has hoped to restore its diminished Middle East role through the Geneva conference of which it is cochairman with the United States. Moscow evidently fears that the Israeli-Egyptian track could lead to a settlement that leaves it on the sidelines. Habib's trip may be designed to quiet some of those fears.

In the Callagham-Begin talks that ended tonight, the British had hoped to hear what reciprocal "gesture," if any, Israel intended to make to match Sadat's remarkable initiative.

Begin is said to have explained that matters have gone far beyond the stage of gestures, and that a brand new negotiating dynamic had been launched.

In the Israeli view, they have already reciprocated by giving Sadat the Knesset as a platform to express his views to the people of Israel and the world. The central point of Begin's trip here, these sources said, is to make clear that a "whole new ball game" is now being played in the Middle East.

Begin and Callaghan first met Saturday night and the formal portion of the visit ended with a dinner at the Savoy Hotel this evening.

Begin is to remain here through Wednesday, however, meeting with local Jewish leaders, talking to British editors and meeting key figures in Parliament from both the ruling Labor and opposition Conservative Parites.

State Department spokesman Hodding Carter III said in Washington that Habib would be seeing Soviet experts on the Middle East during his two-day visit to Moscow. The visit, Carter said, was not a sudden decision but was "part of a continuing consultation between the United States and the Soviet Union" that has been under way since May.

The State Department said it "rejects categorically" any suggestion that Habib's trip is part of a U.S. or Soviet effort to recapture the initiative in the Middle East peace-seeking effort from Sadat.

Carter pointed out that Habib's talks with the Soviets would be only at the technicians' level and that he would not be seeing Foreign Minister Andre Gromyko.

Habib is scheduled to leave Moscow Tuesday for Brussels where he will join Secretary of State Cyrus R. Vance for talks with NATO foreign ministers later in the week.