President Bush is prepared to offer Soviet President Mikhail Gorbachev assurances about the future of Germany as part of an effort to help him stabilize a Soviet internal situation that appears increasingly desperate, a senior administration official said yesterday.

Chief among the assurances is likely to be a proposal for future negotiations to limit the military forces of a united Germany, which U.S. sources described as a volatile political problem for Gorbachev, adding to his growing economic and ethnic woes. Bush may suggest that a proposal be adopted in the current 23-nation Conventional Forces in Europe negotiations pledging to set treaty limits on German and other European armed forces in a future round of CFE deliberations, the official said.

As the White House prepared for Gorbachev's arrival at 6:30 p.m. today, U.S. and Soviet arms negotiators meeting at the State Department for the third consecutive day settled longstanding issues concerning limitations on the Soviet Backfire bomber, U.S. sources said. The negotiators also made progress toward full agreement on the definitions of tanks and armored vehicles to be limited in a 23-nation treaty now under negotiation in Vienna.

A separate session of other U.S. and Soviet officials agreed to final details of the meetings between Bush and Gorbachev. U.S. officials said there will be six hours of discussions by the two leaders at the White House Thursday and Friday, as well as a full day of talks Saturday at the presidential retreat at Camp David. In addition, the officials agreed to an hour-long meeting of Gorbachev and congressional leaders at the Soviet Embassy and a half-hour meeting with Vice President Quayle, both on Friday.

The latest development in Moscow -- the election of Boris Yeltsin as president of the Russian republic -- added to growing U.S. concern about Gorbachev's internal strength. The administration is increasingly concerned that "a really deep instability" could be ahead for the Soviet Union, the senior official said, raising such issues as future control of the thousands of Soviet nuclear weapons.

Despite Yeltsin's political victory, however, White House officials appear to have little use for him, describing him as an intellectual lightweight and demagogue. Some officials suggested that his emergence as a powerful liberal may enable Gorbachev to reassert a centrist posture between conservative and liberal wings.

"This is not a summit devoted to the celebration of agreements that we can sign. It is a summit designed to do the hard work of trying to overcome the remaining obstacles that stand in the way of transforming East-West relations," said a White House official in the last of a series of briefings for reporters.

Listed as key topics for summit discussion were four major clusters of issues: ending the division of Germany, the internal situation in the Soviet Union, the aspirations of the Baltic states seeking to secede from the U.S.S.R. and arms reductions.

There was little doubt that the future of Europe, especially of a Germany in the throes of rapid unification after 45 years of East-West division, is likely to be the most important topic for both leaders. A Soviet spokesman, Director Georgi Arbatov of Moscow's Institute of the U.S.A. and Canada, predicted that the summit discussions on Germany would be "one of the most difficult, hard conversations" between Bush and Gorbachev.

The United States will stick to its position of backing a unified Germany's inclusion in the NATO alliance, an idea widely supported in the West but strongly opposed by the Soviets, Bush has said. To make this more palatable to Gorbachev, a senior official said, Bush may suggest a "general statement" in CFE I, the conventional forces treaty currently under negotiation in Vienna, setting up a framework for specific limitations on German troops and those of other European nations in the CFE II treaty, which is planned to follow the initial pact.

To adopt detailed limitations on German forces in the current round of negotiations, the official said, would be to reopen nearly completed deals and "really stretch {them} out" into a "whole new negotiation."

A State Department official said it has become increasingly clear in Soviet discussions with Secretary of State James A. Baker III as well as with European diplomats that Moscow is placing high priority on guarantees that limitations on the German armed forces will be adopted. The Soviets want the "certainty" of such limits as part of the price for agreeing to overall cutbacks in the conventional military forces of East and West, the official said.

A Soviet official in Washington to prepare for Gorbachev's visit said Moscow sees no reason to delay assurances about German forces to the next CFE treaty. "What is the logic about the next round? We would prefer to see earlier discussion" of such limits, the official said.

The Soviet official also said he would be "very much surprised" to see agreement on Germany reached during the summit, saying that the prospects are better for an eventual accord, after many future discussions, involving "a complicated formula" for Germany's future.

In addition to the suggestion about setting up a framework for eventual German force limits, the senior administration official said, Bush may offer Gorbachev "some understanding about the period of time that the Soviet troops could stay in East Germany and the circumstances of their removal."

Bush will also be ready to talk to Gorbachev about possible changes in NATO's military strategy, including the longstanding "flexible response" in which nuclear weapons back up conventional forces, the official said.

Another U.S. official said Bush will offer Gorbachev a flexible "transition period" to new security arrangements for Germany and urge the Soviet leader to take advantage of West German offers to subsidize Soviet troops in East Germany. Bush may also suggest that West Germany can be a source for the investment capital that the Soviet Union badly needs, the official said.

U.S. sources predicted that Bush and Gorbachev will be able to announce agreement on the main points of the Strategic Arms Reduction Treaty (START), which has been under negotiation since 1982 and which the two leaders hope to sign before the end of this year.

Soviet officials who briefed reporters said they detected optimism among Soviet negotiators who have been working on arms issues at the State Department since Sunday. Like their U.S. counterparts, however, the briefers declined to provide details.

State Department spokesman Margaret Tutwiler, commenting on a Washington Post report that the Soviets have begun to dismantle their long-disputed radar station at Krasnoyarsk in Siberia, said, "we have indications that preparations are underway to begin dismantlement." She declined to be more specific.

Staff writers Ann Devroy and David Hoffman contributed to this report.

Today: 6:30 p.m. -- Mikhail Gorbachev arrives at Andrews Air Force Base.

Thursday: 10 a.m. -- Arrival ceremony at the White House. Gorbachev meets with President Bush. 7 p.m. -- State dinner at the White House.

Friday: 11 a.m. -- Gorbachev meets with Bush at the White House. 6 p.m. -- Signing ceremony. 7:30 p.m. -- Gorbachevs host dinner for the Bushes at the Soviet Embassy.

Saturday: 9:30 a.m. -- Bush and Gorbachev leave by helicopter for Camp David.

Sunday: 10 a.m. -- Bush-Gorbachev news conference. Noon -- Gorbachev departs.

SOVIET EMBASSY

Gorbachev will stay here during his visit.

MADISON HOTEL

Members of the Soviet delegation will stay here during the visit.

SOVIET COMPOUND

Members of the Soviet delegation will stay here during the visit.

LIBRARY OF CONGRESS

The Gorbachevs are expected to take a tour to view Russian history books sometime during their visit.

LAFAYETTE SQUARE

Various demonstrations throughout the visit.

THE ELLIPSE

Various demonstrations throughout the visit.

STREET CLOSINGS: 16th Street between L and M streets will be closed from 7 p.m. Tuesday to 11:59 p.m. Sunday. Northbound traffic will be diverted at L Street and southbound traffic will be diverted at M Street. Also, the service roadway on 16th Street between Scott Circle and M Street will be closed.

In addition, one or two lanes on 15th Street NW between L and M streets will be closed on the Madison Hotel side of the street.