The Catholic bishops are doing a brave yet questionable thing. They are forcing a public debate on perhaps the most perplexing nuclear question of them all, the morality of the doctrine of nuclear deterrence -- on which rest, like it or not, the security of the United States and the nuclear peace of the world.

Twenty, ten, even three years ago, you might have fit most of the people prepared to debate this question into a seminar room. But then came the derailing of SALT II, Afghanistan, Poland and the rise to power of a president determined to reassert America's ostensibly lost power, and now you need a stadium.

Or a big church. The bishops, speaking for and to a large mainstream mass-membership institution, are pressing an anxious public and a reluctant government to treat explicitly a question that has heretofore been left in the shadow and that may have no new satisfactory answer now.

Deterrence says to the Soviets, if you attack us or our allies, we will inflict upon you "disproportionate" and "unacceptable" damage. It has worked in the sense that the nuclear peace has held. But many people are increasingly fearful that it won't and that, anyway, the costs are too high. The bishops, drawn to the issue by "this terror in the minds and hearts of our people," find deterrence only "marginally justifiable" -- as a way station on the path to general disarmament.

The bishops accept that deterrence may prevent others from using their nuclear weapons. But they gag on the disproportionality and unacceptability of the damage threatened. That is, they turn from deterrence precisely for the qualities for which successive administrations have embraced it. Where the bishops think it may be wrong to brandish this specter, the government thinks it would be perilous not to. One feels deterrence will unleash the dogs of war, the other that it will cage them.

The anxiety controlling the administration is that the Soviets will attack or intimidate us. Hence deterrence is strategically necessary and morally right. From the bishops' controlling anxiety, war, flows their conviction that deterrence is strategically and morally dubious.

The bishops are not simply arguing, as many others are, against particular Reagan pronouncements and programs -- wishing to "prevail" if war comes, building the new MX missile, and so on. Their logic and passion have taken them to the very foundation of American security policy. And they are doing so on a basis -- a moral basis -- that admits of little compromise, once you accept it.

By adjusting on arms and arms control, the administration could probably deflect the pressure of the bishops and their like, but it is bent on not adjusting -- at least not yet. Nor at its highest levels can it field anyone to address these issues with a command of them equal to their importance.

Instead, it complains that the bishops pay insufficient heed to its arms control proposals, and it suggests that they may be undermining deterrence by conveying to the Soviets a misleading idea about our firmness.

In a democratic society professing to be guided by certain values, it cannot be wrong to demand that public policy be measured against those values. Those who demand, however, must address the practical, political dimension of the problem whose moral dimension intrigues them, and they must look at all aspects of that moral dimension.

That we have hooked ourselves on a doctrine that "threatens the created order" makes unhooking necessary but not easy. If deterrence does not justify every weapon and war plan hatched in its name, a condemnation of deterrence does not justify every change hatched in its name. There is a threat of war. There is also a Soviet threat. Do the bishops have a view of it?.

Our strategy has arisen chiefly from strategic, technological and political considerations. But it is not bereft of a moral side. Defending freedom, though not everything done in its name, is moral. Aiming at enemy forces rather than populations is moral, though populations would not go free. Trying to build or negotiate smaller, safer forces is moral, though not every proposal rates that imprimatur. Avoiding war, whether by deterrence or disarmament, is moral.

The full force of our country's moral tradition ought to be trained on these grave questions, and the political leadership ought to struggle honestly with them. The specific answers may not be so important as the sense that we are morally as well as politically engaged.