Soviet leader Mikhail Gorbachev's latest move in arms control leaves a major obstacle to a U.S.-Soviet treaty banning medium- and shorter-range nuclear missiles. But the shape of a compromise down the road is evident to some U.S. officials and independent experts.

Gorbachev's willingness to eliminate the last 100 medium- range missile warheads in Asia, as announced in Moscow Wednesday, is a large part of what the Reagan administration had hoped would emerge from an expected mid-July meeting here of Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze. The Shevardnadze mission evaporated a few weeks ago, and forward motion in the Geneva negotiations halted.

The unilateral Gorbachev move puts the drive for an INF (intermediate-range nuclear force) treaty back on track in unexpected fashion, but with 72 aging U.S.-West German weapons more prominent than before as a serious hurdle.

Why did the Soviets pause and then move on?

Former secretary of state Henry A. Kissinger, expressing a view also held by some in the White House, said Moscow halted to see whether President Reagan would be demolished by the Iran-contra hearings and then moved ahead after the Soviets concluded Reagan will survive the testimony of former national security adviser John M. Poindexter.

A senior U.S. arms control expert, however, believes the halt was due to a policy review in Moscow of its arms negotiating positions and that the Gorbachev announcement was made in the normal course of events when the policy review was complete.

Still others said the elimination of nearly all obstacles except the one that is most sensitive in West Germany is Moscow's way of causing maximum trouble within the NATO alliance.

The United States and the Soviet Union have been pursuing an agreement since 1981 in hopes of eliminating a volatile political issue in Europe. Although the agreement would cover less than 5 percent of the superpowers' nuclear arsenals, both sides have hoped it would lead to a separate pact on reducing strategic nuclear stockpiles and lessen East-West tensions.

The obstacle at the top of a list offered by the Soviets Thursday is the West German Pershing IA missile, an obsolescent weapon whose nuclear warheads remain in U.S. hands.

The Soviets insist that these warheads, like all others of its class in U.S. and Soviet inventories, be eliminated. Mainly because of West German sensitivity, Washington has insisted they be excluded from any deal.

Especially since Gorbachev made his move, U.S. officials have emphasized their refusal to bargain away the Pershing IA warheads, citing long-established principles governing arms control positions of the western alliance.

But further inspection suggests room for compromise if Washington and Moscow are willing to bargain and Bonn is willing to cooperate.

A senior U.S. official familiar with arms control issues said yesterday the principles included:A refusal to negotiate about "third-country systems" not controlled by either nuclear superpower. Under this rubric, the United States has consistently -- and successfully -- maintained that British and French nuclear forces cannot be included in U.S.-Soviet deals. Insistence on maintaining existing "patterns of cooperation" between Washington and its allies. The U.S. warheads for the West German missiles are described as part of this pattern.

The official said that British, French and West German backing for these principles makes it impossible for the United States to accept the Soviet demand for elimination of the Pershing 1A warheads.

"Everybody in NATO would be furious if we began talking to the Russians about the {weapons} systems of other NATO members," the official said.

The allies, especially the British, also would vigorously object if the existing pattern of U.S.-German military cooperation were to be disturbed, the official added. One reason is that a planned $13 billion sale of U.S. Trident submarine missiles to the British has been justified as stemming from such a "pattern."

The solution to the problem is thought by some administration officials to lie in the fact that the 15-year-old West German missiles will become obsolete in about three to seven years unless they are modernized. Under the treaty being discussed, the period for reductions would be five years, which is roughly the same.

Thus an "understanding" or side agreement -- possibly based on a unilateral West German statement -- that the Pershing IAs will not be modernized would have the effect of eliminating them, almost as surely as if they were explicitly banned by the treaty.

It could be argued that such an accord would not conflict with U.S. and allied principles, the senior official said, explaining that "we've made no commitment with respect to a new type" of missile. He thus drew a distinction between abandoning an existing agreement and an arrangement which looks only to the future.

This is admittedly "a narrow line" of argument, the official said, and one that has not been accepted within the administration at this point. But it would seem to open the way to a compromise solution of the sticky Pershing IA issue.

The West German government thus far has made no commitment to modernize the Pershing IAs and is divided on whether to keep such an option.

The Soviets, having just eliminated one important roadblock and having spotlighted the troublesome Pershing IA issue, are thought to be in no hurry to make a new concession regarding these weapons in Germany.

"If the Germans were to agree with us that this is all right, then it would be practical to do it," the senior U.S. official said.

But the Reagan administration is reluctant to take this or any other Pershing IA compromise to the West Germans because of criticism U.S. officials attracted after pressuring Bonn last month to accept elimination of all short-range as well as medium-range missiles.

Thus neither side can be expected to move quickly, and probably not before the Shultz-Shevardnadze meeting that is now likely when the Soviet minister comes to the U.N. General Assembly in late September.