One welcome casualty of the hostage affair is the notion that power is something prey to abuse at American hands. President Reagan could yet abuse it, of course, in the sense that American power was widely thought (earlier, anyway) to have been put to wrongful purposes in Vietnam, Yet it seems gratuitous to admonish him so soon on this score. The need, rather, is to see him use power skillfully, well.

Jimmy Carter wanted a government "as good as its people." He often an apologetic or guilty attitude, a premise of American fallibility, toward the use of power by the United States. True to his lights, he returned to Plains reaffirming his own "constant restraint in the face of severe provocation."

Ronald Reagan might say he wanted a government as brave or as strong as the American people. He takes for granted that power is there to be used and hints at no moral qualms about its exercise. To show constant restraint in the face of severe provocation, he might say, correctly, is to invite further provocation, perhaps worse.

That President Reagan was elected to offer something other than constant restraint goes without saying. Even without the hostage crisis, he would have had a license to find early and auspicious occasion to flex American muscle. But that does not mean, I think, that he is authorixed simply to go out and bash somebody. That might raise as many questions about his judgement as it would answer about his will. The country does not have the luxury of allowing him to demonstrate only the latter, notwithstanding the current permissive mood.

Actually, Reagan may be in the situation of not having to make such a demonstration. Whatever it is that bestows credibility -- character as much as conduct -- Reagan plainly has. Theaya-tollah himself has just validated the verdict handed down by the American electorate last Nov. 4

In this regard, the hostage crisis could be prophetic. True, it was, from one point of view, too easy. On the merits, the United States was completely in the right, and almost everyone in the world thought so. Iran's war with Iraq and its internal convolutions, moreover, had put Iran in a mood to look for a way out.

For all that, Reagan played his part beautifully. I am not (yet) one of those who can tell when he's scowling for real and when he's acting, but obviously he put the fear of God in the Iranians. Sending signals is only one part of diplomacy; arranging terms of accommodation is another. The hostage denouement needs to be understood as a combined Reagan-Carter act. But Reagan certainly sent the right signals the right way.

He seems unlikely to evince much of the Carter tendency to regard diplomacy as non-military piece-fitting, an activity hermetically sealed from any local or strategic balance of power. A contrary tendency, to pass by too quickly the requirements of fitting nations' interests to each other, is something I wonder about more.

It is all very well to say that the American bargaining position must be strengthened. Carter, ultimately, bought that. The question remains whether the new president has a reliable sense of where he wants the United States to end up in the world.

The question is framed sharply by his inaugural vow to "maintain sufficient strength to prevail if need be, knowing that if we do so we have the best chance of not having to use that strength." The insistence that weakness tempts challenge and miscalculation cannot be faulted. But his assumptions that the United States could in some meaningful sense "prevail" in a nuclear war, and that the Soviet Union could be brought to accept that American posture, are only that: assumptions, highly debated, highly debatable. The real transition, from slogans to concrete reality, remains unconsummated.

Indeed, across the whole superpower board, Reagan has positioned himself better to compete that (assuming the competition is succesful) to coexist. This is basic. Restoring formally the linkage of political to strategic questions loses much of its purpose unless there is some guiding concept of what the final political relationship is supposed to be. Expecting Moscow to abide by American "rules of conduct" becomes merely a formula for protracted conflict -- perhaps the Kremlin will make it that regardless -- if Moscow is not consulted in drawing up those rules.

It is not enough just to change the core premise from deep-down-we're-compatible to deep-down-we're-not -- a shift the Kremlin surely sold to most of the last Americans holdouts, by the way, by its unforgivable last-minute attempt to queer the release of the hostages. But outrage and vigilance are only half a policy. It's the other half that President Reagan has yet to show.