It is being noted that the Reagan administration has softened the tone of its nuclear rhetoric in order to allay the earlier concern here and in Europe that it planned actually to fight a nuclear war, not simply to deter one.

The tone is softer. The new annual Pentagon "posture statement" does not read, as last year's did, as though Caspar Weinberger had just run up a flight of stairs. The document, The Wall Street Journal reports, even borrows warnings from the Catholic bishops' pastoral letter against using nuclear weapons "deliberately for the purpose of destroying civilian populations." The Pentagon is on the alert against wayward words that feed public anxiety.

No doubt there are internal documents extant that, if leaked, will rekindle public concern. Ronald Reagan himself could do the job of an afternoon with a single breezy remark. Soviet propaganda and our own careless political debate will do their separate bits.

The administration is smart, however, to try to lick a problem that has plagued its diplomacy and domestic composure for two years: its penchant for scaring people about nuclear war.

But is it a con job? Is the administration merely changing the face of a still- dangerous policy, in which case the public is poorly served by the new discretion, or is it removing the provocative gloss from a policy that was never as bad as it was cracked up to be?

The administration, says Weinberger, has no illusions about the dangers of nuclear war, and believes that neither side would "win." That formulation is presumably for the critics, who have feared that the administration, ostensibly believing that winning is feasible, would thus sooner go to war.

Whether "the administration"--a term of uncertain meaning in this context--actually ever meant such a thing is arguable. In any event, "winning" is now a dirty word. But certain war-fighting objectives, not new to this administration, remain: "to restore peace on favorable terms," "terminating the conflict and reestablishing deterrence at the lowest possible level of violence . . ." What does this mean?

Many people take the view that once the first bomb goes off, doomsday has arrived, and if everyone, including the Russians, feels that way, then deterrence will hold. The administration, however, is not sure the Russians feel that way. It fears that the Russians, more able than we are both to inflict and to incur casualties, might turn our fear of doomsday against us and seek advantage from nuclear blackmail.

Thus, the administration concludes, we should be seen to be able to conduct a flexible nuclear response. It means, accordingly, to project a readiness to accept the use of nuclear weapons but depending on circumstances to start small in the hope, though not the certainty, of avoiding escalation.

In his latest report, Weinberger cites the similar commitments to starting small made by former defense secretaries Robert McNamara, James Schlesinger and Harold Brown. His point is fair: to contest the notion that this administration has concocted new and unprecedentedly dangerous war-fighting plans.

When Reaganites talk about starting small, of course, alarms start buzzing. Reagan's real nuclear troubles date from his suggestion in 1981 that a limited nuclear war in Europe might not grow--a conventional and innocent observation that the European press and others played as a cynic's readiness not only to countenance nuclear war but to let Europe endure the effects of one alone.

A libel, this reading ignored the steps the United States has taken over the years --the latest is the Pershing II-cruise missile program--to reinforce deterrence by linking our nuclear fate with Europe's. Nor do many Europeans and Americans credit this administration's attempts to raise the nuclear threshold by improving conventional preparedness.

In sum, the Reagan administration, in its steadier moments and precincts, differs from its predecessors not in being more war- minded but in being more worried that deterrence might fail. Hence its readiness-- for the purpose of strengthening deterrence --to advertise its preparations to fight a nuclear war. Hence the self-generated pressure --again, to strengthen deterrence--to indicate that if it did fight a nuclear war something worth saving could be saved.

I am disturbed by a "doctrine" that contemplates, for whatever reason, going nuclear. But I am also disturbed by a common attitude that attributes to a Kremlin dictatorship the same anti-war constraints that operate in an American democracy. We should never stop arguing and puzzling over these awesome weapons. But we should do so soberly and honestly.