Egyptian President Anwar Sadat yesterday urged Israeli Prime Minister Menachem Begin to be more flexible in his peace negotations, but he said that Defense Minister Ezer Weizman is welcome to return to Cairo "whenever there are new ideas."

Weizman, viewed by some as Begin's growing political rival, visited Egypt last week and met twice with Sadat, although he apparently made no progress in the informal talks.

The Egyptian leader, speaking to an international group of journalists and academics, also said he was pleased with U.S., participation in Middle East diplomacy and said President Carter "really has taken his share."

"The American role is very important because America and President Carter are no more mediators, he is a full partner. He has agreed on his conception and, for me, this is very satisfying," Sadat said.

Carter and Begin disagreed over the terms of a settlement during the Israeli leader's visit to Washington last month, largely over Begin's interpretation of U.N. Resolution 242 specifying Israeli withdrawal from territory occupied during the 1967 war.

Replying to a questioN, Sadat said, "I have taken more than my share (of initiatives). I fear that any other initiative is just putting the cart before the horse. How can we open new exchanges when (until) now we speak two different languages."

Meanwhile, Israeli Foreign Minister Moshe Dayan returned to Tel Aviv from Bucharest, expressing satisfaction over his talks with Romanian President Nicholae Ceausescu.

Dayan said he had never hoped to persaude Ceausescu to change his position on total Israeli withdrawal from the occupied territories, but he said the Romanian leader had encouraged Israel to continue direct negotiations with Egypt.

Before leaving Bucharest, Dayan said Israel expects a U.S. peace initiative soon. He said the Israeli government was waiting to hear from Secretary of State Cyrus Vance within the next month on details of the negotiating process.

The foreign minister said he told Ceausescu that the Palestine Liberation Organization is absolutely unacceptable" to Israel as a negotiating partnr because, "It is like asking us to negotiate with the Nazis. We take them as a bunch of murderers."