THE MEDICAL component of international relations, specifically, of Soviet-American relations, has been too little noted. This is a feature of the scene that became prominent in the first Reagan term and is apparently bound to be no less prominent in his second.

You know what we mean. In the first term, Soviet-American relations were horrible, and arms control was going nowhere. There were various explanations, but one favored in the White House started from the fact that the leaders in the Kremlin were old and sick and kept dying. The president himself repeatedly lamented that he had confronted an unprecedented difficulty in his approaches to the Soviet Union: he had had to deal with three Soviet leaders (Brezhnev, Andropov, Chernenko) in a very short time. The transitions, he indicated, kept the Kremlin in a constant state of agitation, and it was hardly fair to blame the White House for the poor foreign policy results.

All this came to mind the other day when we read, courtesy of Reagan administration sources, the latest medical bulletin on Soviet President Konstantin Chernenko. Suffice it to say that the poor fellow is apparently in dreadful shape with irreversible emphysema. He may be meeting his maker within months, or sooner, or later. In any event Ronald Reagan will be meeting his fourth Soviet counterpart. At first glance, the news looked grim, in different ways, for both of them.

But what's this? The administration believes, the story said, that Chernenko's health will not affect forthcoming armscontrol negotiations with the Soviets, and certainly not in the short run. American officials, the story went on, have noted that relations between the two countries appear to have stabilized. So perhaps it won't matter for the United States one way or the other just how the redoubtable Mr. Chernenko fares.

Well, we have a view of this latest use of a medical gambit in political analysis. The doctors of Kremlinology in the Reagan administration were almost certainly wrong the first time when they tried to attribute the deterioration in superpower relations to the state of the Kremlin's health. They could be wrong the second time in their evident determination to play down the effects of mortality in high Soviet places.

In the first instance the administration, needing to explain trouble, wanted to show there was no Soviet partner. In the second, hoping to keep up momentum, it wants to show there is a Soviet partner. The plain fact is that the Americans don't know and the Soviets don't know just what will come when Mr. Chernenko goes. Cheerful speculation that everything is on a steady course should not be allowed to interfere with careful attention to what actually happens.