MOSCOW, JULY 20 -- U.S. and Soviet officials now agree that negotiations in Geneva on a medium-range missile accord have stalled in recent weeks, but they disagree over who is to blame and what should be done to revive momentum toward an agreement that could pave the way to a superpower summit.

Significantly, Soviet sources here portray the Geneva talks to eliminate U.S. and Soviet missiles from Europe as already having resolved the most important military details. They assert that the last few snags are "artificial" ones that could quickly be cleared away -- if the Reagan administration would show the political will to do so.

The key to the Soviet approach seems to be a new willingness by the Kremlin to wait out the White House in the belief that the president's stature and influence are waning. Tactically, this approach would appear to leave the Soviets well positioned to force Washington to make the remaining concessions that would nail down the accord.

U.S. officials assert that Moscow has suddenly and inexplicably called a halt to significant progress in U.S.-Soviet negotiations. They cite a slowdown at the Geneva talks and the absence of any response to invitations for Soviet Foreign Minister Eduard Shevardnadze to visit Washington for meetings that could remove the final obstacles to a deal on missiles based in Europe.

Western diplomats, concerned that an opportunity to conclude a U.S.-Soviet arms agreement might be slipping away, have warned that the Soviet Union is taking a risk by slowing the pace of negotiations with a new wave of hostile talk.

Soviet officials respond that the atmosphere in Washington has been marred by the Iran-contra affair and the rise of "right-wing influences" and is not conducive now for high-level talks between the United States and the Soviet Union. Valentin Falin, information director for the Soviet press agency Novosti, contends that President Reagan and his aides seem to be basing their commitment to the Geneva talks on whether "it helps or hurts" their public image in the Iran-contra affair.

But in interviews here, both Soviet and western arms control experts concede that negotiations in Geneva or at a higher level can probably remove the remaining hurdles in the path of a pact on European-based missiles. These differences focus on choosing the best method to verify an agreement, as well as the fate of 100 warheads that Moscow proposes to exempt from the treaty and leave in Soviet Asia and 72 West German Pershing IA missiles that carry U.S.-controlled nuclear warheads.

Soviet military spokesman N. Lebedyev dismissed these issues as "artificial" in an appearance here last week. He said that the military aspects of the prospective treaty are essentially settled and sounded optimistic about the chances for concluding an agreement.

The Soviet Union signaled its willingness to resolve the biggest difference over an intermediate-range nuclear missile treaty during informal discussions that U.S. officials here say took place last spring in Geneva.

The officials said that Soviet Col. Gen. Nicholai Chervov floated a compromise deal to settle key differences in the European missiles talks, but Soviet officials have since dismissed the report as "rumor."

Having displayed its flexibility in the talks on medium-range missiles with the reported overture, the Soviet Union now appears to be mounting a strategy for negotiating concessions on other issues considered more crucial.

According to Soviet officials interviewed here, the coming battles with the United States now loom over the terms for third summit meeting between Reagan and Kremlin leader Mikhail Gorbachev, tentatively planned for this fall in Washington, but still under discussion.

The Soviets also are looking toward possible compromises between the two sides over space-based weapons and cuts by both sides in strategic nuclear arsenals, as well as potential agreements on other strategic issues such as a Soviet proposal to reduce and eventually eliminate nuclear testing on both sides.

Falin, stressing that "we have only two or three years left for serious arms control efforts," said in an interview last week that the Soviet Union is still interested in achieving the objectives outlined at the Reykjavik summit last October.

At that summit, Moscow proposed limiting research on space-based weapons and gradually eliminating nuclear testing as well as deep cuts in medium-range and strategic nuclear arsenals.

Following meetings that Secretary of State George P. Shultz held here in April, the Soviet Union said that a summit meeting could consist of making final an intermediate nuclear force agreement (INF) and forging key conditions for agreements on cutbacks in strategic weapons, nuclear tests and limits on space research.

In the hope of achieving these goals within the two-to-three-year period identified by Falin, which would include the last phase of the Reagan administration, the Soviet Union has apparently developed a strategy consisting of the following elements:Taking a wait-and-see attitude toward the summit and the arms talks while the Reagan administration, as Moscow sees it, sinks deeper into the Iran-contra morass, gradually losing its overall influence.Cultivating closer relations with U.S. allies such as Britain and West Germany, which may prove helpful in influencing the Reagan administration during presummit negotiations. During a visit to the Soviet Union by West German President Richard von Weizsaecker last week, Moscow took two steps to forge closer ties with Bonn: lifting a veto on a long-planned trip by East German leader Erich Honecker to West Germany to take place in September and expressing new interest in a meeting next year between West German Chancellor Helmut Kohl and Gorbachev.Highlighting what they call inflexible aspects of Washington's arms control policy before the world public by mounting a campaign of attacks against the Reagan administration's positions.

While Soviet strategy is largely oriented toward achieving medium-term goals, it also has short-term objectives, according to western diplomatic analysts here. In particular, they say, the Soviets are seeking to pressure the North Atlantic Treaty Organization to adopt a more conciliatory position on remaining obstacles in talks to eliminate medium- and short-range missiles, such as including the 72 West German Pershings -- with their U.S. warheads -- in the proposed treaty.

Soviet officials have described U.S. and West German objections to such a move as the biggest barrier to an INF agreement, but they have indicated in talks with U.S. officials here that the issue must be resolved in talks on a higher political level than the Geneva arms negotiations.