BONN, AUG. 25 -- Foreign Minister Hans-Dietrich Genscher is seeking to commit the West German government not to modernize Bonn's 72 antiquated Pershing IA missiles and thus remove one of the last obstacles to a U.S.-Soviet arms control treaty before Secretary of State George P. Shultz and Soviet Foreign Minister Eduard Shevardnadze meet in Washington next month.

Genscher's position, which was put forward in the past two days by spokesmen of his Free Democratic Party, represents the first firm indication that West Germany might back down from its insistence on keeping the Pershing IAs.

In Moscow, senior Soviet diplomats warned today that the Shultz-Shevardnadze talks are still jeopardized by the dispute over the West German Pershings. {Details on Page A20.}

The Soviets have said that the U.S.-controlled nuclear warheads on the Pershing IAs must be destroyed if the proposed treaty is to be adopted. The pact would scrap all of the superpowers' intermediate-range missiles -- those with ranges of between 300 and 3,500 miles.

The Pershing IAs, with a range of 460 miles, fall in the category of weapons to be destroyed. But the United States has insisted that they are West German weapons and therefore are outside the scope of a bilateral U.S.-Soviet accord.

Genscher favors allowing the West German-owned missiles and their U.S.-controlled nuclear warheads to be dismantled in the early 1990s, when they are scheduled to be scrapped anyway because of obsolescence, according to sources close to him. He proposes that no new missiles similar to the Pershing IAs be deployed as long as the planned U.S.-Soviet treaty is in effect, the sources said.

The foreign minister, who represents the moderate wing of Chancellor Helmut Kohl's center-right coalition, would like the government to make the no-modernization pledge before East German leader Erich Honecker visits Bonn Sept. 7 and the scheduled meeting a week later between Shultz and Shevardnadze.

The West German pledge, in Genscher's view, would remove the danger that Shevardnadze might call off the meeting in Washington because of the Pershing IA dispute, as the Soviets have threatened.

While concerned about the strategic impact of eliminating all short- and medium-range nuclear missiles from Central Europe, Kohl's ruling coalition also wishes to avoid any blame for delaying a disarmament accord because it wants to keep the Pershing IAs. Two state elections are scheduled for September and opinion polls show the prospective arms deal is popular with voters.

Genscher's position set the stage for the second major showdown in four months within the West German government over its position on the proposed U.S.-Soviet pact. Genscher won the previous battle when the government agreed in June to support a broadening of the treaty to include weapons with ranges of between 300 and 600 miles as well as those in the 600- to 3,500-mile range.

Some prominent conservatives in Kohl's coalition have strongly opposed promising not to replace the Pershing IAs with modern weapons. Alfred Dregger, parliamentary leader of the Christian Democratic Union-Christian Social Union alliance, said last week that such a pledge was "out of the question."

Other leading conservatives have said privately, however, that they were certain that the issue would be resolved as Genscher favors. "I am afraid the hard-liners are going to suffer another loss," a high-ranking conservative politician said.

Kohl has repeatedly declined to make a clear commitment about the future of the Pershing IAs. He may do so at a news conference scheduled for Wednesday, or during a parliamentary debate on the issue on Sept. 2 that was scheduled at the insistence of the opposition Social Democrats.

Genscher has gone on the offensive because a letter from Shultz and other recent statements by U.S. officials led him to believe that Washington expected Bonn to take the initiative in resolving the dispute, the sources said.

Genscher has not publicly outlined his position, because to do so would draw criticism from conservatives that he was speaking without government authorization.

But two disarmament experts in his party -- Uwe Ronneburger and Olaf Feldmann -- outlined the no-modernization proposal in public statements this week. The sources close to Genscher said Genscher fully supported their statements.

"The position of the Free Democratic parliamentary group is clear: we are not clinging to the 72 missiles. The problem will take care of itself by 1992," Feldmann said in an interview with the daily Koelner Express.

The no-modernization proposal has been suggested widely as a solution to the Pershing IA dispute, but no leading West German official previously had embraced it.

The Soviets have rebuffed another suggested deal on the Pershing IAs, under which the missiles would be scrapped in exchange for cutbacks in the Soviets' arsenal of Scud missiles, which have a range of under 300 miles.

Genscher is convinced that Bonn has to take the initiative on the Pershing IAs because of repeated U.S. public and private statements that Washington would stick by its ally even at the cost of sacrificing an arms control agreement, the sources said.

"They didn't press us, but we understood the Americans to say very clearly, make up your mind what you want to do about the Pershings," a Bonn official said.