Israeli Foreign Minister Moshe Dayan held-talks yesterday in Bucharest with Romanian President Nicolae Ceausescu in a new effort to break the Middle East stalemate.

Romania, the only Communist nation having relations with both Israel and the Arab world, has long made itself available as a conduit for negotiations, and Dayan's meeting came amid reports that Palestinian leader Yasser Arafat planned a visit to Bucharest soon.

Moreover, Ceausescu is scheduled to visit Washington next week, and Romanian sources said the president specially wanted to talk with Dayan before leaving for the United States.

Israeli officials in Jerusalem said there was absolutely no connection between Dayan's talks and Arafat's scheduled visit, and they said there was "not even a remote possibility" that they would meet in Romania.

Officials said Dayan gave Ceauseseu a personal message from Israeli Prime Minister Menachem Begin, but both governments declined to say what it contained.

Ceausescu was credited by Egyptian President Anwar Sadat and Begin with helping to arrange Sadat's historic visit to Jerusalem last November.

Before he left for Bucharest, Dayan criticized Egypt for failing to come up with any positive peace proposals as alternatives to those put foward last week by Israeli Defense Minister Ezer Weizman in Cairo. Yet, in Cairo, Sadat yesterday praised Weizman as someone sincerely seeking peace.

Meeting with reporters during a tour of an agricultural project in the western desert, Sadat was asked to compare Weizman with Begin. The Egyptian leader said, "I don't want to make a comparison. Everyone has his personality, but Weizman is sincere for peace, and I like the man."

Meanwhile, the Israeli military command said that Israel has begun a gradual "thinning out" in southern Lebanon, but that it will keep troops in the occupied area south of the Litani River for about another month, or until U.N. peackeeping forces finish taking up their positiones. The statement was the first official confirmation that a withdrawal had begun, although there have been reports of an Israeli pullback.

An army spokesman said the movement of troops and armor out of the area began about a week ago and is being timed to coincide with the entry of U.N. soldiers from Norway, Sweden, Iraq, France and Nepal. At the United its planned 4,000-troop peackeeping force is on station in southern Lebanon.

U.N. Secretary General Kurt. Waldheim reported in New York that about 3,000 peacekeeping troops will be in place by next week. Israel, which reportedly put about 5,000 troops in Lebanon, has said that it will completely withdraw when the U.N. force is fully deployed.

In Lebanon, the Norwegian troops coming down from Beirut were greeted by chants of "Long live the United Nations," and "We like Waldheim" at Sidon, a coastal city 25 miles south of Beirut that has received many Moslem refugees from the fighting.

Israelis and the Christian Lebanese in the occupied area have said they fear that the U.N. troops will not be able to keep the guerrillas from returning to positions they lost in the south.

The top leader of Lebanon's rightwing Christian militias, former president Camille Chamoun, called yesterday for the French to increase their contigent in the U.N. force to 5,000.

France is the traditional protector of Christians in Lebanon, a former French mandate, and the Christians want a French-dominated U.N. force to act as a "deterrent strike force" to reinstate security throughout Lebanon following the breakdown of the 1975-76 civil wear.

As Lebanese leaders in Beirut insisted on more U.N. troops in the border area, the leftist newspaper as Safir said neither Syria nor Lebanon expects an early Israeli pullout from South Lebanon.

As Safir said the Israelis were strengthening their positions in the south and that the Lebanese government was considering another appeal to the U.N. Security Council - either directly or through Waldheim - to ensure an Israeli withdrawal.

Elswhere, President Mohammed Daoud of Afghanistan urged Moslem nations to unite to regain Jerusalam's Al Aqsa mosque" by force if necessary," Saudi Arabian state radio reported. The mosque, one of the three holiest shrines of Islam, has been under Israeli occupation since the 1967 war.