A curious inversion of roles has overtaken the country's nuclear debate. President Reagan and his lieutenants are no longer making hair-raising statements about fighting, surviving and winning a nuclear war. Now the stirring of nuclear alarms is being done by the anti-war crowd. It is constantly evoking catastrophe in terms that are, I fear, hysterical, misleading and bad for our political health.

I should say right off that the president's real policies, as distinguished from his thoughtless observations, have not changed. His military budget and posture and his approach to arms control are still guided by the same fearsome, exaggerated view of Soviet capabilities and intent. But he has sworn off the pronouncements that so aroused the European peace movement and that -- in a chance chemical reaction with Jonathan Schell's "The Fate of the Earth" -- created an American peace movement in the last two years.

Reagan raised nuclear alarms in the name of stiffening deterrence -- as though Moscow needed to be warned that we mean business. Pure in heart, the anti-war people do it, to no less gratuitous and mischievous effect, in the name of preventing war. Take, for instance, Ground Zero's Roger Molander: "Nuclear war could conceivably happen tomorrow -- even today . . . Even slight changes in any one of several current world crisis situations could bring the superpowers into direct conflict and create the risk of a nuclear holocaust."

But no. This is, I think, an appalling remark from a nuclear sophisticate like Molander, a leap from reality to anxiety, from a proper vigilance into an unseemly panic.

Ground Zero hopes to communicate to election candidates that "the prevention of nuclear war is of serious concern to citizens" and to assist "both candidates and citizens in structuring an effective approach to the problem of preventing nuclear war."

Well, one can fairly ask whether war is best deterred by this or that configuration of forces, diplomatic strategy, or set of words. One can observe that Reagan spoke foolishly and released the fears that many people carry around with them just under the skin. But to suggest that Reagan takes nuclear war casually is, I submit, absurd. It is more accurate to say he has his own dubious notion of deterrence. If he were truly casual, he should be impeached.

As to "structuring an approach to prevent nuclear war," demonstrably the United States and the Soviet Union are very good at it: so far, Hiroshima aside, their record in preventing nuclear war is perfect. What they are very bad at is preventing conventional war. The two may not be entirely unrelated. Governments figuring to make war can do so with knowledge that the great powers' care about escalation gives the conventional warriors room to maneuver. If another Hiroshima is your nightmare, then worry first about Pearl Harbor, the start of a conventional war.

The Ground Zero theme that nuclear issues must be removed from the experts, and from government officials, to the people also energizes Common Cause. Chairman Archibald Cox declares: "A thoughtful, concentrated and organized people's movement is the best, if not the only, way to impel government to press imaginatively, wholeheartedly, urgently and persistently for an international agreement reducing nuclear arms."

I am one of those who wish there were a "people's movement" in the Soviet Union, but never mind. It is simply not true that in nuclear matters the people are disenfranchised. A "thoughtful, concentrated and organized people's movement" concerned with, among other things, nuclear war put Reagan in the White House -- the Republican Party. Reagan is pressing now for "an international agreement reducing nuclear arms" -- START. Common Cause is going to have to penetrate beyond the pieties to make an effective nuclear mark.

"At another critical time," adds the group's president, Fred Wertheimer, "we helped turn the concerns of millions of Americans into effective legislative action that finally ended the Vietnam War." But what Congress ended was not the war in Indochina but the American part in it. The war went on, killing and brutalizing millions. Vietnam is not the precedent I would cite to draw citizens into another grand confrontation.

So, you may say, trendy populism is not the worst thing going, Reagan's policies could destroy us all. To which I say: then challenge them. But challenge them soberly and in a manner likely to produce serious results. Otherwise risk the early dismissal of the issue as nuclear chic.