Secretary of State Cyrus R. Vance was scheduled to leave Washington last night for what he described as "a searching exchange of ideas" for peace in the Middle East.

Vance's first stop on his initial diplomatic mission as secretary is Israel. He then travels to Egypt, Lebanon, Jordan, Saudi Arabia and Syria in a crowded, eight-day trip.

The United States welcomes Soviet cooperation in resolving the Arab-Israeli conflict, Vance is an interview with members of the Israeli press made public last night.

Vance said he has discussed his mission with the Soviet Union, which he said has "a vitally important role" as co-chairman, with the United States, of the Geneva conference on the Arab-Israeli dispute.

The key obstacle for covening a Geneva conference is how it will approach the problem of what U.S. officials call "the legitimate interests of the Palestinian people."

At a Washington news conference yesterday, retired Israel army Maj. Gen. Matti Peled said there are "convincing signals" that the Palestine Liberation Organization may be ready to recognize Israel.

Peled has been involved in unofficial talks with the PLO. His previous claims that the PLO is prepared to abandon its demand for eliminating the state of Israel and replacing it with a secular state have been strongly challenged by other Israelis.

Nevertheless, "a very positive development can be expected" from the PLO "if we do something to encourage it," Peled said at a news conference sponsored by the American Friends Service Committee.

As Vance prepared to leave Washington a State Department spokesman said one of many issues he will explored will be Israeli oil-drilling in the Gulf of Suez, which the United States considers illegal.

According to published accounts, Israel may be close to a major oil discovery off the western shores of the Sinai peninsula, which it captured from Egypt in the 1967 war.

State Department spokesman Frederick Z. Brown said the continuing U.S. position is that "Israel, as an occupying power, does not have the right to exploit natural resources in occupuied territories that were not already being exploited when the occupation began."

The American position, Brown said, is that such an operation "is not helpful to get peace negotiations under way, and complicates a settlement."

Another Carter administration envoy, Washington attorney Clark M. Clifford, is to leave today on a peace-seeking mission. Clifford, who was Secretary of Defense under President Johnson and earlier served President Truman, is President Carter's special envoy in the Greek-Turkish clash over Cyprus. The dispute is still unresolved after the 1974 warfare between Turkish Cupriots and Greek Cypriots, during which Turkey occupied a large portion of Cyprus.

New talks between Greek and Turkish Cypriots have just opened up, encouraging prospects for a Cyprus settlement. Clifford, on a 10-day trip, will stop first in Vienna to see U.N. Secretary General Kurt Waldkheim, who laid the groundwork for the recent talks.

Clifford is scheduled to be in Athens Feb. 18; Ankara, Turkey, Feb. 21-22; Nicosia, Cyprus, Feb. 23-25, and then in London before returning to Washington March 1.