Indicating disagreement with the core proposal of the U.S. Middle East peace plan, Egypt said today that it does not consider President Reagan's call for a self-governing Palestinian entity federated with Jordan to be a "positive element."

Speaking at a press conference for foreign correspondents, Egyptian Foreign Minister Kamal Hassan Ali also reaffirmed Egypt's refusal to resume talks with Israel on Palestinian autonomy unless Israel pulls back its troops from Beirut.

The tone of Ali's comments appeared to be at variance with those made last Saturday in Paris by Egyptian President Hosni Mubarak, who said that Egypt planned to give the Reagan initiative "as much support as we can and encourage the United States to go ahead with the peace process."

Observers here speculated that the toughening was in reaction to today's Israeli advance into West Beirut and that Egypt was seeking to protect itself from fresh Arab criticism for being the only Arab country to maintain diplomatic relations with Israel.

Ali seemed to indicate that Egypt was at odds with another key Arab friend of the United States, King Hussein of Jordan, who Monday said that he favored the federation idea as put forth by Reagan and indicated that the time for new negotiations was close at hand.

Egypt's interpretation of the Camp David accords has been that the initial five-year period of Palestinian autonomy is preparation for self-determination leading to an independent Palestinian state instead of an entity linked to Jordan. In his speech Sept. 1 outlining his plan, Reagan ruled out U.S. support for such a state.

With Egypt and Jordan taking significantly different positions on the objective and timing of autonomy talks, it was not immediately clear how the peace process could be relaunched, particularly since Reagan has reaffirmed the Camp David process as the framework for proceeding. Egypt was one of the three signatories of the accords, which call for Cairo to be involved in any talks on Palestinian autonomy.

Ali said that Egypt was concentrating on the "positive elements" in the Reagan plan. When asked whether Egypt considered the president's call for a federation between Jordan and a self-governing Palestinian body in the West Bank and Gaza Strip as one such element, the foreign minister replied curtly, "No."

Ali said that Egypt would make known its views at forthcoming talks with the Reagan administration.

Ali was categorical about Egypt's refusal to consider any resumption of U.S.-sponsored autonomy talks in the current circumstances, although he characterized the Reagan initiative as a "most important and constructive contribution" and said the Middle East was on "the threshold of a new, major effort" to find a lasting settlement.

He called for an end to "all hostilities" in Lebanon as "the first element" necessary to get autonomy negotiations going again, saying, "In an atmosphere of war, you cannot seek your way to peace."

Later, he added more emphatically, "You cannot start negotiations when the Israelis are occupying an Arab capital." He also called for a "clearcut commitment by Israel to withdraw all its forces from Lebanon according to a fixed timetable," acceptance by Israel of "the cessation of all settlement activities" and the implementation of unspecified confidence-building measures in the occupied West Bank and Gaza Strip.

Without these, he said, there was no hope for success of "any endeavor," although he did not say specifically that Egypt was making these three points preconditions for undertaking renewed talks on the Palestinian issue.

Ali said Egypt believed the peace process should be expanded and include "all the countries around Israel," apparently referring to Lebanon and Syria as well as Jordan.

Ali's comments stood in sharp contrast to the general air of optimism created by King Hussein in an interview with the British Broadcasting Corp. aired late Monday. The king said that the time was coming "soon" when negotiations would take place and added:

"I believe that what will finally emerge is some form of plan for a federation -- between Palestine and Jordan -- that Jordanians and Palestinians will have to either accept or reject."

He proposed that Jordanians and Palestinians vote in a referendum on the federation "at an appropriate moment" and predicted that the Palestine Liberation Organization "will cease to exist and the Palestinians will present themselves to the world in a different way."

The king gave no indication that he thought the Israeli invasion of Lebanon and occupation of Beirut were serious obstables to resuming negotiations. He indicated that he thought the Reagan proposals were a good basis for talks, calling them "the most courageous stand taken by American administration since 1956," when then-president Eisenhower opposed the joint Israeli-British-French attempt to seize control of the Suez Canal.

Asked if the latest summit of Arab leaders had given him a mandate to enter the U.S.-sponsored peace process now, the king replied, "No. That has not been the case so far as the Fez summit is concerned. The Rabat summit still holds."

This was a reference to the Arab summit held in Rabat, Morocco, in 1974, when Arab leaders endorsed the PLO as the "sole, legitimate representative" of the Palestinian people. This effectively barred Jordan or other Arab nations from undertaking negotiations on behalf of the Palestinians. The king apparently is considering avoiding this barrier by submitting anything he may negotiate with Israel and the United States to a referendum.