MOSCOW, SEPT. 1 -- A senior Kremlin official said today that a treaty on the elimination of medium and short-range missiles could be achieved only if the United States agrees to extend the ban to include its nuclear warheads on West Germany's 72 Pershing IA missiles.

Deputy Soviet Foreign Minister Alexander Bessmertnykh, in a press conference, also discussed other issues tying up the negotiations for the treaty, now in their final stages in Geneva, including a dispute over methods of verifying the accord.

Bessmertnykh said the prospect for a summit meeting between Kremlin leader Mikhail Gorbachev and President Reagan hinges on progress in the negotiations for the agreement. "As to whether a summit could be possible without an agreement," he said, "I would say that this is not possible."

He also sounded a note of pessimism about the arms talks, in contrast to other official Soviet assessments that a new position on the Pershing IA missiles taken by West German Chancellor Helmut Kohl last week had brightened the prospects for an agreement.

In response to Moscow's insistence that the Pershings should not be excluded from the treaty under discussion Kohl last week pledged to allow the obsolescent Pershing IAs to be phased out and not replaced if the other terms of the accord are decided between the United States and the Soviet Union. The treaty would eliminate the two countries' ground-based nuclear missiles with a range of between 300 and 3,500 miles.

The Pershing IA missiles are under control of West Germany but their nuclear warheads are under U.S. control. They were deployed in the late 1960s and were scheduled to be replaced with more modern weapons in the 1990s.

"The West German statement contains a number of positive elements," Bessmertnykh said, "but unfortunately it has not moved the talks forward in Geneva." He added later that Washington should agree to specify in the treaty that the Pershings will be eliminated and Bonn should be more specific in its stance against the missiles.

Bessmertnykh's pessimistic tone contradicted assessments of the progress in Geneva given by other Soviet officials and seemed to reflect a fledgling strategy to step up pressure on the United States and its allies on the arms talks.

He said strategic issues will likely consume the "lion's share" of talks between Soviet Foreign Minister Eduard Shevardnadze and Secretary of State George P. Shultz, due to begin in Washington Sept. 15. Bilateral, human rights and regional issues will also be discussed, he said.

Other Soviet officials have indicated that negotiators in Geneva have concluded as much as 70 percent of the agreement and have been significantly buoyed by Kohl's statement of last week.

In a press conference in Warsaw today, for instance, Soviet Foreign Ministry spokesman Gennadi Gerasimov said that Kohl statement had brought about "improved chances," for an agreement. "We are more optimistic than a week ago," Gerasimov told journalists.

The two sides differ over several aspects of the verification of a treaty, Bessmertnykh said. He said Washington objects to inspections in third countries that might be affected by the accord, while Moscow favors such inspections.

He said the two also differ over the timetable for dismantling the missiles. Washington favors having Moscow dismantle its missiles until the two sides have an even number, after which the United States would begin dismantling its missiles.

The Soviet Union has now proposed that both sides disconnect launchers from warheads simultaneously, Bessmertnykh said.

"We're not happy or comfortable with the U.S. position that the need for verification will be nonexistent after the elimination of medium- and short-range missiles," he added.

Another key issue is how to go about destroying the stockpiles of missiles, western diplomats said. "It is necessary to work out a strict and rational system of verification," he said, "a system that would provide complete confidence that the weapons to be reduced and destroyed will really be reduced and destroyed."