BONN, JULY 5 -- West German President Richard von Weizsaecker flies to the Soviet Union Monday for an official state visit viewed here as confirmation that relations between Bonn and Moscow finally are poised for a sustained improvement.

The chief of state's trip could mark the breakthrough in Soviet-West German ties that Chancellor Helmut Kohl's center-right government long has desired but been unable to attain, according to West German officials and western diplomats.

Moscow has kept Bonn at arm's length diplomatically since West Germany's 1983 decision to deploy U.S. medium-range missiles. A thaw in relations a year ago ended abruptly in November when Moscow strongly protested Kohl's comment in a magazine interview in which he appeared to compare Soviet leader Mikhail Gorbachev's public relations skills to those of Nazi propaganda chief Joseph Goebbels.

Today, however, prospects have brightened for better relations because of the overall improvement in the East-West climate resulting from progress toward a U.S.-Soviet agreement to slash intermediate-range nuclear missile arsenals, the officials and diplomats said.

An announcement is expected during von Weizsaecker's six-day trip of a firm date for a long-awaited visit to West Germany by Soviet Foreign Minister Eduard Shevardnadze, West German officials said. He probably will come in September or early October, they said.

Chief government spokesman Friedhelm Ost said Friday that von Weizsaecker's trip is "a visible sign of sustained improvement in German-Soviet relations."

Von Weizsaecker, whose duties are largely ceremonial, will be the first West German president to visit Moscow since 1975. He will meet Gorbachev on Tuesday in Moscow and later will go to Leningrad and Novosibirsk, in Siberia.

Von Weizsaecker said last week that he plans to emphasize long-term improvement of relations. He specifically will raise the issue of how West Germany can use its economic muscle to help Gorbachev's modernization program and thus improve overall ties between the two countries, according to his aides.

West Germany has played a leading role among western countries in encouraging the West to lend Gorbachev active support for his reform program. Bonn's policy has been crafted by veteran Foreign Minister Hans-Dietrich Genscher, who will accompany von Weizsaecker to Moscow.

The government's approach is designed in part to improve bilateral ties with the Soviet Union and thus undercut the claim by the opposition, the left-of-center Social Democratic Party, that it alone can foster better relations with the East Bloc.

Bonn also would like Moscow to give a green light to East Germany to improve relations between the two Germanys. East German head of state Erich Honecker said recently that he "probably" would make a historic first visit to West Germany before the end of this year. But he requires Moscow's approval to do so.

Von Weizsaecker said he will raise the issue of inter-German relations with the Soviets, even though he knows that it is an "uncomfortable" topic.

Von Weizsaecker would prefer to avoid discussing specific disarmament issues, but the Soviets are expected to reaffirm their objection to the North Atlantic Treaty Organization's position favoring the continued presence of Pershing IA missiles in West Germany even after similar weapons are barred from Europe by the expected U.S.-Soviet arms control treaty, West German officials said.

West Germany and the rest of NATO contend that the Pershing IAs are West German systems and thus are not affected by the proposed pact, which applies only to the superpowers' missiles. The Soviets maintain that the Pershing IAs' warheads, which are under U.S. control, must be removed as part of the bargain.

The case of maverick aviator Mathias Rust, 19, the West German pilot who was jailed on May 28 after penetrating Soviet air defenses and landing a small plane in Red Square, is not expected to be resolved during von Weizsaecker's trip, West German officials said.

Bonn has said it is satisfied with the way that Moscow is handling the case, and West German officials said they were eager to prevent it from becoming an obstacle to better relations.