Reagan administration officials, discounting reports of either a breakthrough or a breakdown in the Beirut negotiations, said yesterday that preparations are continuing at a steady pace for deployment of a U.S. force to assist in the peaceful withdrawal of Palestinian guerrillas besieged by Israeli troops.

Tight-lipped officials had little to say in public amid a welter of confusing and often conflicting reports about the status of the negotiations and about the potential involvement of 800 to 1,000 U.S. Marines in policing the evacuation.

"I'm not going to characterize the situation in terms of progress or lack of progress," said State Department spokesman Dean Fischer, adding that the situation is too fluid for such a judgment.

Official sources reported that there are major unsolved problems in several areas. The most pressing were reported to be the withdrawal arrangements for Palestine Liberation Organization fighters and the creation of the temporary multinational force to oversee the operation and help the Lebanese government restore order.

Some differences were reported to remain between the United States and Israel after a fresh exchange of correspondence between President Reagan and Prime Minister Menachem Begin. Among these, according to a source familiar with the exchange, is Begin's continuing rejection in his letter of a residual PLO military or political presence following the withdrawal of most guerrillas.

The exchange, which was initiated by Reagan Wednesday, covered the denial of food, water and electricity to the beleaguered civilian residents of West Beirut, as well as other issues.

Reagan reportedly said major U.S. efforts were being made to achieve peace, citing the activity of special envoy Philip C. Habib and the offer to involve U.S. forces, and called on Israel to make corresponding efforts.

Begin, in his reply Thursday, reportedly said the blocking of supplies and power into West Beirut had been ended. There were some disagreements between the two leaders about tactics, but not about overall objectives, the source said.

Among the array of problems facing officials were these:

* Continuing U.S. public and congressional concern about the use of American troops or ships in the evacuation operation.

The White House is summoning the bipartisan congressional leadership to a meeting Tuesday afternoon to explain the need for U.S. participation and advance the process of consultations required by the War Powers Act.

In a letter to Reagan, Rep. Clement J. Zablocki (D-Wisc.), chairman of the House Foreign Affairs Committee, called on the president to give official notice to Congress of the deployment of U.S. troops under a clearly binding section of the act. Zablocki said he had been "disturbed to learn" that Reagan is planning to notify Congress under an alternate provision which would not limit the use of the forces to 60 days in the absence of a declaration of war or congressional endorsement.

Another congressional problem is the position of Senate Majority Leader Howard H. Baker Jr. (R-Tenn.). According to an aide, Baker does not oppose use of the U.S. Sixth Fleet to transport or escort departing PLO troops but he continues to oppose entry of U.S. troops to Lebanese soil.

Emerging doubts about the participation of France, which was expected to be the other major participant in the multinational force to police the withdrawal.

One requirement of Reagan's conditional approval of the use of U.S. troops last Friday, according to a senior White House official, is that another nation join the force. U.S. sources said French President Francois Mitterrand had indicated "an approval in principle" of his nation's participation in early discussions, but that "implementing discussions" have not been completed between Washington and Paris.

The U.S. sources said the PLO, with a substantial degree of French support, is asking the United Nations to play a role in authorizing or at least endorsing such a multinational force. Washington sees a U.N. role to be impractical, especially after the objection to American troop participation lodged by Soviet President Leonid Brezhnev in a letter to Reagan and publicized by Moscow.

The suddenly clouded issue of Syria's willingness to be the initial destination of departing PLO fighters, many of whom are expected to continue from there to other Arab or Islamic nations.

Washington officials said they were surprised by today's Syrian news agency announcement that "there is no chance to transfer the Palestinian fighters from Beirut to Syria." The officials here said no such rejection of a temporary refuge role had been received or indicated through diplomatic channels.

The Syrian press statement came just as Deputy Assistant Secretary of State Morris Draper, Habib's assistant, was arriving in Damascus to brief the Syrian government on the Beirut negotiations and plans for the PLO withdrawal. It was uncertain whether the Syrian press statement represented an authoritative and current position.