IN some respects, the Soviet Union, or what's left of what used to be the Soviet Union, is a bigger challenge to American foreign policy today than it was in the worst times of the cold war. At least then we knew what we wanted to do, and it was fairly easy to tell if we were being successful. But now our interest is discernible only in the most general terms, and it is even less clear what we might do to advance that interest.A good deal of the confusion arises from the fact that there are two revolutions: One is political; the other, economic. There is a temptation for policy analysts to consider them separately, but any American policy based on purely political or purely economic considerations is going to be be unrealistic and lead to failure. The political revolution has already brought about the collapse (or at least the discrediting) of the Communist Party, what may be the beginning of the reorientation of the KGB in ways that are still difficult to fathom, and related ferment associated with glasnost. It has also seen a process of political fragmentation as constituent republics declare their independence - the three Baltic states, the Ukraine, Armenia, Kazakhstan. Who knows where it will end? In the pre-Gorbachev era, all of these things would have been cause for joyous celebration in the United States. Now we are not so sure. It is good to have the Communist Party in the dustbin of history. But is it really good to have six or eight or more new states to deal with, all of them weak, inexperienced, and facing multiple difficulties? We need to approach these evolving situations with a firm sense of the limits of our own influence. This is not to disparage efforts to use what influence we have; it is only to recognize our modest capabilities. This has an important corollary: Efforts to influence the situation beyond our capacity are quite likely to be resented and counterproductive. The economic revolution is another story. The old order was not overthrown so much as it collapsed; now a new order has to be erected on its ruins. In the meantime, what passes for an economic system is extraordinarily creaky, inefficient, and unproductive. The requirements for capital and for know-how are enormous; all the capital and know-how available in Western Europe, North America, and Japan could disappear in a black hole if care is not taken. There are two complications for the US. First, we have so mismanaged our own economy that we have no money. We continue to spend it as though we did have it - in rescuing our financial institutions from the consequences of their bad judgment and in piling up deficits of $300 billion a year - but we would be hard pressed to mount an additional major foreign aid program. SECOND, officials of the Bush administration seem not to grasp either the dimensions or the nature of the problem. They talk about how there have to be reforms, about how market forces have to be given free play, about how belt-tightening measures have to be adopted. This is all very well; but it is how people in Washington talk about Brazil or India, and we are dealing with a problem infinitely more complex. There does have to be a plan. There does have to be a conversion to a free market. There does have to be currency reform. And all of these changes have to take account of the fact that it is not one centralized country any more. It would be very difficult to know what to do even in the best of circumstances, even if the US were as preeminent as it was in 1947. Western Europe then did not face half the difficulties that Eastern Europe does today, and it still took a year just to get the Marshall Plan off the ground. Thanks in major part to the success of the Marshall Plan (and to the rehabilitation of Japan), the US does not have to play as large a role now as it did then. There are European and Japanese resources and know-how available. Further, American, European, and Japanese interests converge. We do not need a grand blueprint for what Russia and surrounding countries will look like in 2040. That is something they will work out for themselves and it will probably be quite different from anything we might imagine today. What our interests do require as a minimum is that the situation not fall further into chaos with attendant opportunities and temptations for tinpot demagogues and other would-be successors to Lenin and Stalin.