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THE post-Reykjavik discussion about what President Reagan may have finally settled with General Secretary Mikhail Gorbachev - an end to ballistic missiles or all strategic offensive weapons - carries on. From its drift, it appears that moral issues may once again be sidetracked in the name of the ``metapolitics'' of nuclear deterrence - a precept based on the utility of useless force. The morality of threatening unimaginable destruction of mankind as the basis for international peace had been challenged earlier than Reykjavik, by the American Roman Catholic bishops as well as by the President and general secretary. At long last it appeared as a central issue in the waning hours of conversation at Hofdi House between the world's two most powerful leaders. Failure of the follow-on talks at Vienna only underscores the urgency of this moral issue.

Predictably, the nuclear deterrence establishment expressed shock. Its reaction resembled opposition to the bishops' earlier proposition that nuclear weapons constitute the wrong military policy - morally and technically.

Reagan should not let what was attempted in the final hours at Reykjavik slip away into the hands of a nuclear deterrence mandarinate skilled at exploiting the paradoxes of the atomic age.

The case for defense based on nuclear deterrence rests on two things: the absence of general war between the US and the USSR since 1945, and the protection of allies against Soviet intimidation. Yet on those few occasions when the two great powers have gone to the brink of conflict, it was to the edge of nuclear, not conventional, war. Some experts on deterrence doubt the presence of nuclear weapons helped much to resolve these crises, and such arms do not guarantee cautious superpower behavior in the future. What actually deters has proved a nagging question in the postwar period. It is not readily answered by the presence of nuclear weapons alone.

Fear has arisen in West European circles, encouraged by some in the American military establishment, that the last hours at Reykjavik signaled a decoupling of American strategic weapons from Europe's defense. Yet so many nuclear weapons exist in the European theater that they guarantee that any armed conflict between NATO and the Warsaw Pact will escalate into full-scale atomic war - like some awesome fuse lit near the frontier between East and West Germany at the moment of initial impact between the opposing forces. So lazy has thinking grown under this metapolitics of nuclear deterrence that instant collapse - or ``unacceptable attrition'' - of NATO conventional arms seems almost certain. So heavily does NATO's current strategy of ``flexible response'' rely on nuclear deterrence that some see it as a recipe for automatic atomic war.

Would not the very certitude of nuclear war deter a Soviet attack on NATO? Most agree that the answer would depend on the nature of the East-West crisis that may threaten war, not on the certainty of nuclear escalation. Since history never repeats itself, no one knows what the next crisis will bring or what it might portend in the way of hostility between the two nuclear giants. In other words, what has deterred world war so far may have nothing to do with the coupling of US strategic forces to Europe's defense; it may be the effect of the absence, to this point, of a crisis serious enough to trigger such a catastrophe. Is stable deterrence, in any event, much more than a transitory phase in US-Soviet nuclear relations?

Can a defense policy ostensibly based on the inadmissibility of world war through nuclear deterrence, which is actually more dependent for its success on the seriousness of a given political crisis, be morally justified? Can it honestly be said that future trends in nuclear arms technology, if left to their own logic, will provide much in the way of stable military expectations for crisis management?

The answer on both counts is ``no.'' This double negation underlies the final hours of Reykjavik and the tentative commitment of both leaders to early elimination of all strategic offensive weapons. This determination should be pursued with urgency on both sides.

The only military experience with nuclear weapons occurred at Hiroshima and Nagasaki. All strategies of deterrence since 1945 have been based on a metapolitics involving only 40 years of postwar history. Deterrence is largely hypothetical, only in part understood by military-affairs specialists, psychologists, and theologians.

Reagan's support of total elimination of offensive strategic weapons - even all ballistic missiles - at Reykjavik has provoked a disquieting opposition, backed by bipartisan consensus.

Has nuclear metapolitics - a notion that the United States cannot use nuclear arms and yet cannot manage its national security without them - provided the basis of national defense policy all along?

Having released the atomic genie in 1945, do we now have some peculiar attraction to global holocaust as a pragmatic and moral policy for our nation?

Opponents of eliminating nuclear weapons argue that the US - for the purpose of deterrence - needs such weapons worse than the USSR. This suggests a nihilistic testimony to our leadership of Western civilization: We seize on the most absurd manifestations of our technology as security for our advanced culture, and consign the Soviets to superiority in the relatively backward reliance on conventional force. Great effort has gone into rationalizing this technological wizardry in the name of mankind's highest values. Mankind deserves better.

Robert J. Pranger is resident scholar in international studies, at the American Enterprise Institute.