Absent Andropov

Exactly a year ago today Leonid Brezhnev's 18-year rule ended, its highlight the brief tryout of detente in Soviet-US relations. Now the tenure of his successor, Yuri Andropov, has apparently turned fragile, as the Soviet President's conspicuous absence from public view for health reasons makes clear.

The prospect of yet another change in the Soviet command should call for greater prudence in the United States and its Western allies in coming weeks. That means both in talks and in deeds, as the period of uncertainty develops or passes. But the silence in the West on a Soviet succession is as notable as Andropov's disappearance from public sight.

It seems strange, at the least, to hear Washington speak of the Soviets these days so uniformly in terms of Soviet aspirations on Grenada or in Lebanon, or in the excoriation shorthand of Korean Air Lines Flight 7, without taking into account the more significant fact of Andropov's possibly tenuous hold on power.

Western Kremlinologists see the Soviet bureacracy itself as already turning cautious. Policies on vital issues like the arms talks in Geneva are likely to continue on their present course. Soviet responses have already slowed down because of Andropov's health. Continuity, not new Soviet initiatives, is expected. Andropov had largely just picked up where Brezhnev left off on various intermediate nuclear force (INF) and strategic arms reduction talks proposals. So far as we know, he has been neither more nor less flexible than Brezhnev on arms.

In the US, where Congress is wrapping up its defense spending plans, the greater uncertainty about the Kremlin command, if anything, likely secures the administration's defense budget. Defense plans, like supertankers, carry a heavy momentum and shift by very small amounts at any given time. The only expected change will be a supplemental outlay for forces in Grenada. But one wonders: Shouldn't the prospect of an imminent Soviet leadership change be a time for Congress to send some signal other than that the US will add $124 million for nerve gas to its quarter-trillion-dollar fiscal l984 defense bill, as the Senate did this week? Congress, too, seems unable to deal directly with any openings a leadership change could offer.

Are governments on both sides of the Iron Curtain so fossilized that the opportunities of change are ignored or are seen as threatening?

As it is, both the US and the Soviet command have apparently concluded that the US will deploy its Pershings and cruise missiles in Western Europe, and the Soviets will respond. The Soviet response has likely been arrived at by consensus and will be carried on however limited Andropov's involvement in coming weeks. The slowing of NATO deployment might have been considered by other Washington administrations, but not this administration, committed to showing the Soviets that NATO has the resolve to deploy.

Whatever hopes the Soviets had a couple of years ago that West European public opinion might force a deferment of deployment was evidently gone a couple of months ago. The expected Soviet response is to discontinue INF talks and begin steps toward countermeasures. These include (1) deployment in Eastern Europe, likely Czechoslovakia and East Germany, of shorter-range nuclear missiles; (2) introducing ground-based missiles in Europe comparable to those of the West; (3) resumed deployment of SS-20 missiles in Europe; and (4) closer to the US, something like sea-launched cruise missiles already in the test phase. The Soviet tendency has been to develop longer-range sea-launched missiles that could reach the US from remote waters. Now they may seek something comparable to the West's cruise with a ''ten minute'' strike-time capacity.

In the Middle East, it could be argued that the Soviet generals' caution in a time of transition would make them less likely to respond to an American-Israeli retaliatory strike. A strike back of Syrian lines in Lebanon might not call for a direct Soviet involvement. But if third parties in response were to attack, say, American naval forces offshore, involving missiles in Damascas, events could escalate dangerously. What the Soviets would do then defies easy anticipation.

At the least, Andropov's public absence should be pushing Congress, the White House, and the West to rethink the possibilities of situations all parties seem to assume are already frozen for the winter.