It is no more than a hunch, but remember, as they say, where you heard it first: in a matter of months, or at least within the next year or so, we may well be witnessing the first serious American debate in a decade on the wisdom of maintaining 300,000 U.S. troops in Europe.

And the worst of it is that the content, if not the outcome of the debate, may be determined not so much by our own free choice as by how well the Soviets play their side of the negotiations getting under way in Geneva on intermediate- range nuclear weapons in Europe.

The Reagan administration's opening "zero option" proposal would appear to offer only one of two prospects: either the Soviets dismantle their SS20s and some other nuclear rockets (SS4s and SS5s) aimed at Western Europe, or the United States will deploy offsetting Pershing IIs and cruise missiles along NATO's front line.

In reality, the alternatives are not nearly so clear-cut. And the stakes go well beyond warhead counting. Hanging in the balance at Geneva is the fundamental nature of the alliance relationship.

Given the numbers game, it will probably be months before both sides work their way through the first step of deciding what should be counted in or out in establishing the existing balance (or imbalance): bombers with dual conventional and nuclear capability or sea-based nuclear forces, for two examples. Only then will it be possible to tackle the business of bargaining out a mutually acceptable new balance.

In the meantime, NATO is operating under a "double-track" agreement reached in December 1979. While the palavering winds on in Geneva, the United States will be moving toward its planned deployment of the Pershings and cruise missile by 1983. This is supposed to keep the pressure on Soviet negotiators.

But it also proceeds from a practical calculation. NATO's conventional forces in Europe (including those American troops) are overwhelmingly inferior to comparable Soviet conventional forces. They are, accordingly, considered inadequate as a deterrent to a conventional Soviet attack, unless reinforced by an intermediate range nuclear force on the Western side, comparable to the Soviet SS20s.

Let's suppose that the Geneva negotiations drag on with the usual hints and planted progress (or no- progress) reports right up to the target date for the first Pershing/cruise deployments. There will be scapegoating, all around. The magic of Ronald Reagan's "bold" initial offer will almost certainly have worn off.

So it is not too much to stipulate, assuming at least some show of Soviet reasonableness, that, at best, the European resistance to the NATO nuclear deployments will remain no less intense than it is today. The Soviets, who were winning the "peace" argument before the Reagan "zero option" offer, may well have regained the initiative.

Come deployment time for the American intermediate-range nuclear forces, you can pretty much count on continuing public pressure on political leaders in Europe to hold off just a little bit longer, the more so if European "neutralists" or "pacifists" can point convincingly to some sort of "progress." Drawn-out negotiations, then, are no guarantee against a hardening of opposition on the part of the countries that matter--West Germany, the Netherlands, even Italy--to any more nuclear weapons, under American control, on their soil.

What then? We come back to the imbalance of conventional forces that gave rise to the whole idea of matching the Soviet SS20s with Pershingcruise missile deployment. The logical answer, as Rep. Les Aspin argued in The Washington Post, is that "if the Europeans want to reverse field and stop relying on nuclear weapons . . . (they) should realize that means heavier outlays for conventional forces or no defense at all."

But "anti-nuke" isn't the only tide running in Europe. Economic distress and perceived neglect of welfare programs are producing powerful resistance to "heavier outlays" for defense of any sort. If that continues to hold true, at what point might we expect the revival of the spirit that gave rise a decade ago to the campaign by Mike Mansfield, then Senate majority leader and now ambassador to Japan, to begin a phased withdrawal of at least half of the American forces in Europe? At one point, he had 51 senators with him.

A lot of congressmen will tell you that a similar spirit of "unilateralism" or "neo-isolationism" lies only just beneath the surface today. For the United States, Aspin argued, the issue would become the safety of our troops in Europe. This opens yet a third prospect if the Geneva venture fails. "If we emerge from this exercise with neither nuclear modernization nor higher defense budgets in Europe," he declared, "a proposal to withdraw our troops would go through Congress like a prairie fire."