Special U.S. envoy Robert Strauss conferred with President Anwar Sadat tonight at the start of a new mission to sound out Egypt and Israel on possible U.S. moves to accelerate the lagging Palestinian autonomy talks.

Strauss' trip to Cairo and Jerusalem, coming three days after Sadat's summit conference in Haifa with Prime Minister Menachem Begin of Israel, was depicted as an information-gathering effort aimed at giving President Carter a direct report on the Haifa discussions.

"I gave Bob all the details to put our friend President Carter in the full picture," Sadat said to reporters after their 75 minutes of sometimes animated talks against a backdrop of floodlit Pyramids.

U.S. officials traveling with Strauss made it clear that he also was taking the temperature in Cairo and Jerusalem for possible new U.S. suggestions designed to broaden the autonomy talks and move them beyond procedural matters that have occupied negotiators so far.

The officials took pains, however, to avoid giving the impression that Strauss is selling any new American initiative.On his last trip to the Middle East August 17-19, Strauss met opposition from Egypt as well as Israel to a U.S. proposal for a new U.N. resolution designed to draw West Bank Palestinians into the talks.

As a result, the American proposal was scuttled. This time, Strauss seemed to be going out of his way to test the moods of Sadat and Begin after their talks before making any new suggestions.

Strauss first met for about 90 minutes this afternoon with Prime Minister Mustafa Khalil. Tonight he met with Sadat and Vice President Husni Mubarak.

Sadat is known to be cool to any U.S. pressure to broaden the format of the autonomy talks at this stage, feeling along with Begin that the pace set out in the Camp David accords and the March 26 peace treaty should be strictly adhered to.

Reports in Israel say Sadat and Begin agreed that the best course now is to concentrate on areas of agreement in order to let the climate of peace grow, postponing any clashes on areas of disagreement.

Despite their accord at Haifa on supervisory forces for the Sinai and on Egyptian oil sales to Israel, Sadat and Begin remain on opposite sides of a broad chasm concerning the definition and ultimate aim of Palestinian autonomy and the territory it should include.

Strauss and U.S. officials traveling with him stressed that this fundamental disagreement has to be tackled sometime in the near future if the autonomy talks are to avoid the appearance of failure.

"I don't think there's any question that in the next couple of months (the autonomy negotiations) will move to a new stage," Strauss told reporters in the U.S. Air Force plane bringing him from London. They will have to "deal with issues that touch the bone, not the flesh," he added.

It is by avoiding the key issues that the talks have been able to make what procedural progress they have, he said.

In what appears to be a reference to his reported agreement with Begin to follow strictly the program laid down in the treaty, Sadat said: "As I agreed with Prime Minister Begin, and as I told my friend Bob, the Camp David agreements and the peace treaty are the very solid cornerstone for the achievement of the comprehensive peace we have dedicated ourselves to accomplish."

The next full session of the talks, postponed by 10 days, is scheduled for the last week in September at Alexandria, Egypt.

U.S. interest in broadening the talks to include West Bank Palestininas and, if possible, Jordan, stems from wider concerns than those that seem to be animating Sadat and Begin. Washington is known to be paying close attention to the desires of Saudi Arabia, for example, while Sadat recently said Arab opponents to his peace policies would have to come to him if they wanted reconciliation.

Prince Abdullah, deputy Saudi prime minister and head of the Saudi National Guard, underlined the Saudi desires today in a statement calling again on the United States to recognize and deal with the Palestine Liberation Organization.

One outcome of the Haifa talks singled out by Strauss' aides as a subject of special curiosity in Washington was the accord in principle for an Israeli-Egyptian observer force in the Sinai pending formation of an international force in cooperation with the United States.

Israeli Foreign Minister Moshe Dayan, Israeli Defense Minister Ezer Weizman, Egyptian Defense Minister Kamal Hassan Ali and Mubarak all are expected to touch on this problem during visits to Washington in the coming 10 days.

The imminence of their direct talks on the supervisory force -- Mabarak leaves for Washington Monday -- indicated that the main task before Strauss was rather the U.S. effort to encourage movement in the autonomy talks.