Are Soviets replacing their crucial spokesman to West Germany?

Moscow's premier policy spokesman for West German audiences is becoming a media commentator, a move surprising Western diplomats here by its timing. The transfer of Valantin Falin, a seeming demotion, is the latest in a generally cautious series of early personnel shifts by new Soviet leader Yuri Andropov. It also comes as Moscow is escalating its bid to encourage antinuclear sentiment in West Germany, and in Europe as a whole.

Foreign Minister Andrei Gromyko opens talks in Bonn Jan. 17. Formerly, Mr. Falin would have been included in such a delegation. It was not yet clear whether he would be this time, as the announcement of Mr. Gromyko's departure did not say who was accompanying him.

Mr. Falin was ambassador to Bonn during the 1970s' heyday of detente, and has been No. 2 man in the Communist Party's international information department since its founding under Leonid Brezhnev in 1978.

The department head has been Leonid Zamyatin, a close Brezhnev protege and an often acerbic spokesman for Mr. Brezhnev during his trips abroad.

Some Moscow sources say further changes in the department are planned, possibly even its disbanding - a possible development in which, foreign diplomats maintain, the Falin move might be a logical first step.

But senior officials questioned Jan. 13 would not immediately confirm these reports, saying only that Mr. Falin was assuming a post as ''political observer'' on the government newspaper, Izvestiya, a shift not yet made public.

Senior officials have, in past private remarks, sometimes implied strain between Mr. Zamyatin's department and other foreign policy specialists within the party hierarchy and the Foreign Ministry.

Among Western diplomats, Mr. Falin is viewed as a bright, articulate foreign-policy specialist. He has, in recent years, met many European delegations here and has also traveled to West Europe. One diplomat involved in talks including Mr. Falin termed him ''by far the smoothest, most effective spokesman I've met in Moscow - especially for the Germans. . . . He's an expert on the issues involved, not to mention a fluent German-speaker.''

At Izvestiya, Mr. Falin will likely cede much of his former role in framing the public Soviet reply to Western policy moves - a main job, officials say, of Mr. Zamyatin's department. Mr. Falin also seems likely to have less frequent or direct input in the work of the Central Committee secretariat, to which the information group and other specialized departments are attached.

In these senses, Mr. Falin seems to have been demoted.

Still, his exact role will become clear only with time. By past example, senior sources say, ''commentators'' with the experience of Mr. Falin might be asked by the secretariat or Foreign Ministry for policy analysis or to help draft foreign-affairs parts of speeches by Soviet leaders.

A hint of Mr. Falin's position may be whether he has traveled to Bonn with Mr. Gromyko.

While officials say further changes in the senior party apparatus are certain , the pace of early Andropov shifts has seemed deliberate.

Similarly, the leadership passed up its first major opportunity to rehabilitate a figure fallen from favor under Mr. Brezhnev.

Nikolai Podgorny, longtime Politburo member and Soviet president until Mr. Brezhnev assumed that post in 1977, passed on Jan. 11. Announcing this, Izvestiya printed a single paragraph expressing ''sorrow,'' and terming Mr. Podgorny a former president and ''honorary pensioner'' - treatment along the lines accorded Nikita Khrushchev on his passing.