Tokyo worries Soviet SS-20s may swing east

Possible deployment of Soviet SS-20 medium-range missiles in Siberia is viewed here partly as a bid to drive a wedge between Japan and the United States in their military alliance.

Japanese officials are now closely studying Soviet Foreign Minister Andrei Gromyko's remarks made Jan. 17 to his West German counterpart, Hans-Dietrich Genscher, in which he said Moscow was prepared to place missiles that exceed an agreed-upon quota for the European zone back in Siberia out of range of Western Europe.

This is causing deep concern in Japan. Foreign Minister Shintaro Abe said in Washington this week, ''This is what we feared most. Such deployment would result in a major change in the Asian situation and pose a real threat to Japan.''

Mr. Gromyko's statement is taken seriously because it follows reported remarks made by Soviet leader Yuri Andropov to West German Social Democratic leader Hans-Jochen Vogel earlier this month that the idea of redeploying the SS- 20s is under consideration to counter a ''new military base in Japan.''

He apparently was referring to the planned deployment of 48 American F-16 fighter-bombers to a base at Misawa in northern Japan beginning in 1985. The plane's 2,000-mile range brings a number of strategic targets in the Soviet Far East well within attacking range. This aspect has provoked several Soviet protests to Japan since the deployment plan was first announced last September.

The Japanese view is that the F-16s are being deployed to counter the buildup of Soviet forces in the Far East, which has already taken place, including military bases built on disputed northern islands within sight of mainland Japan.

Japanese Foreign Ministry and Defense Agency analysts believe Soviet strategy is intended to:

* Induce Western European countries to make concessions by showing Soviet flexibility with regard to reduction of arms in Europe.

* Postpone the deployment of United States medium-range missiles in Europe by creating a rift between the US and Western Europe.

* Deter Japan from cooperating closely with the United States.

This last point assumes more significance in view of the commitments Japanese Prime Minister Yasuhiro Nakasone apparently made in Washington this week regarding Japan's military role. This includes, in time of emergency, trying to prevent passage by the Soviet Navy through key Japanese straits into the Pacific and overflight of long-range strategic Backfire bombers.

Military analysts say the SS-20, with a range of 2,300-3,500 miles, if deployed in Siberia, could easily hit vital targets in Japan and China.

The strategic significance for China, compared to Japan, is considered much smaller, however, because Chinese territory is vast and the degree of urbanization much less.

This new development is seen as certain to intensify the defense debate in Japan, especially over the issue of the growing cooperation with the US in regional security.

The possibility of aiming new Soviet missiles at the densely populated Japanese archipelago will certainly be cited by those who say Japan is far too involved in ''US global military strategy.''

There has been some opposition to the deployment of the F-16s at Misawa, although it is fairly muted so far. However, opposition is likely to intensify now that Moscow has escalated the war of words.

In the past, discussion of Japanese defense has been on a rather academic, theoretical plane.

But many analysts now say that recent events have brought the entire debate into sharp focus, requiring the Japanese to make a clear commitment concerning the future of Japan's military relationship with the US.