THE bishops of the United Methodist Church, the third-largest church in the United States, recently issued a pastoral letter rejecting nuclear deterrence. Last November, the conference of Roman Catholic bishops, representing the largest church, saw ``increasing evidence that the conditions for the moral acceptance of deterrence are not being met.'' Moral debate about nuclear weapons is inescapable in democracies. Yet, all too often strategists and politicians have treated nuclear ethics in a superficial manner. If our debate is to be informed by moral reasoning rather than mere emotion, we need to focus on five conditions for a just deterrent.
Self-defense is a just but limited cause. We are justified not only in defending our biological survival but in protecting our culture and freedoms. Self-defense, however, must be narrowly defined. A crusade to rid the world of totalitarianism or communism, or to make the world safe for democracy, may seem admirably motivated to us, but hopelessly self-centered to others, and far too risky to accept in a world of nuclear weapons.
Never treat nuclear weapons as normal weapons. This is made difficult by the usability dilemma. If nuclear weapons are regarded as completely unusable, they lose the deterrent effect that is their raison d'^etre. However, to the extent that planning and discussing prevalence in nuclear war encourage the delusion that a major nuclear war is winnable, it is malicious in its effects. The prospects for controlling the use of nuclear weapons in a crisis are too uncertain to allow us to use such strategies without risking millions of lives. US nuclear self-defense must be reinforced, not by plans for winning nuclear war, but by improving conventional forces.
Minimize harm to innocent people. Since innocent people pose no threat, we cannot justify killing them under the moral principle of self-defense. Yet unilateral disarmament would impose a risk of harm to innocent people in this country. Steps that seriously weaken deterrence merely shift risks from one group of innocent people to another and may raise risks to all. We can more safely reduce the risk of killing noncombatants by not aiming our nuclear missiles at Soviet cities. The critical question is whether or not targeting of the cities would seriously reduce the deterrent effect of American nuclear forces. There is little reason to believe that it would.
Reduce risks of nuclear war. ``Hawks'' emphasize calculated deterrence based on rationality. They argue that the best way to avoid nuclear war is to strengthen the US deterrent posture. ``Doves'' fear that piling up weapons may provoke rather than deter an attack. ``Owls'' believe that nonrational factors such as psychological stress and organizational breakdown during crises present the greatest danger. Small measures that might rationally seem to strengthen deterrence may substantially increase risks of irrational war or weaken our ability to terminate nuclear war should it ever start. A recurrent temptation for nuclear strategists is to be too clever by half by developing elaborate strategies based on calculations of rationality. But much of human history has turned upon unanticipated disaster.
Reduce reliance on nuclear weapons over time. Since human beings are fallible, it seems reasonable to assume that nuclear deterrence may someday fail. Nevertheless, we need not draw apocalyptic conclusions. As Richard Garwin has pointed out, ``If the probability of nuclear war this year is 1 percent, and if each year we manage to reduce the probability to only 80 percent of what it was the previous year, then the cumulative probability of nuclear war for all time will be 5 percent.'' President Reagan has based his Strategic Defense Initiative on the desire to escape from the dilemmas of nuclear deterrence. However, escaping from deterrence requires a leakproof defense, not only against ballistic missiles, but also against bombers and cruise missiles. Such a perfect defense seems unlikely. Although the political and social paths to a less dangerous nuclear future lack the glamour of the technological fix, they do not depend on utopian thinking. Competition does not prevent cooperation. When games of competition and cooperation are played over long periods, a strategy of reciprocity is most effective. When the shadow of the future looms large over the present, the incentives for cooperation between competitors are strengthened. On such realistic premises, it is quite possible to construct a gradual improvement of US-Soviet cooperation.
These five maxims of ``just deterrence'' would not solve all nuclear dilemmas. On the contrary, there is no way to avoid complex empirical arguments and often enormous uncertainty. But they can give us a realistic moral basis for judging nuclear policies and a sense of hope rather than alarm or complacency.
Joseph Nye is director of the Center for Science and International Affairs at Harvard University and author of ``Nuclear Ethics.''