The new Soviet leader, Mikhail Gorbachev, said today that it was his impression that the United States was using the Geneva arms talks as a "screen" for pushing through its rearmament program.

Gorbachev's statement did not provide any assessment of the current Geneva negotiations and appeared to reflect Soviet frustrations over President Reagan's successful effort to win congressional endorsement for a new batch of MX missiles.

The comments by Gorbachev, in a letter written to a West German peace group and made public by the official news agency Tass, were his first direct criticism of the Reagan administration since he took power on March 11 following the death of Konstantin Chernenko.

Gorbachev also cited Washington's effort to enlist Western European participation in research programs for Reagan's Strategic Defense Initiative, a space-based missile defense plan, and the continued deployment of new U.S. medium-range nuclear missiles in Western Europe.

"The Soviet-American talks which have begun in Geneva have given rise to many hopes," Gorbachev said. "As far as the Soviet Union is concerned, I can assure you firmly that we are sincerely interested in the successful outcome of these talks and shall work persistently for them to yield positive results.

"It must be noted, however, that things accompanying the beginning of the talks cannot but put one on guard. Already now, as the talks started, one gets the impression from statements by high-ranking representatives of the United States that they need these talks as a screen for carrying through their militaristic programs."

Gorbachev singled out the deployment of U.S. cruise missiles in Belgium as one of negative developments and then said that the continued deployment of Pershing II and cruise missiles in West Germany was a particular source of concern.

The threat of world war, he said, "will grow and not diminish if the deployment of American first-strike nuclear missile systems is continued" in West Germany. "Soviet people see with concern that a war danger for them is coming again from German soil."

"With the talks in Geneva started," he said, posing what he described as a "logical" question, "why deploy ever-new nuclear weapons in Europe and thus compel the Soviet Union as well to take measures in response?"

Gorbachev assured his West German audience that there was no truth to "malicious" assertions that the Soviet Union was using the coming 40th anniversary of the victory over Nazi Germany to stir anti-German sentiments.

The letter, written to the Peace Council of Heilbronn, in Baden-Wuerttemberg, seems to reflect Moscow's new effort to mobilize Western European public opinion behind its peace drive.

So far, there have been no assessments here of the course of the Geneva talks. Two weeks ago, Viktor Karpov, the chief Soviet negotiator, said on Soviet television that the Americans appeared to want to conduct a "seminar" rather than negotiate seriously about banning weapons in space.

But there have been no substantive comments on the Geneva negotiations and Karpov's comments appeared before the two sides presented their basic positions.