WAR IS TOO SERIOUS a matter to be left to strategists who treat it as technicians, sociologists who look for cause and patterns, or statesmen who invariably claim either justice or necessity. If Michael Walzer's beautiful book had no other merit than that of reminding us that war is not simply a scourge like a sudden typhoon, but part of the moral world - a subject for moral judgments, precisely because it is an object of human choices - it would already be useful. But the virtues of the book are far greater and deeper.

Walzer wants to answer the two questions asked by the Christian theologians who fathered the Just War theory, the doctrine which dominated Western thinking until the rise of the modern state. Under what conditions is a particular war just or unjust? This is a matter of ends. How can a war (just or not) be fought well? This is a question of means, and of rules that form what Walzer calls the "war convention" (often codified by international law). His answers derive from a doctrine of rights: the state's right to territorial integrity and political sovereignty, the basic human rights of individuals - life and liberty. Thus, in so far as ends are concerned, aggression is a crime, and the state has a duty to resist it, lest its rights and those of its members be eroded. Concerning means, whereas soldiers, as servants of their political communities, have forfeited their right to live and assumed a right to kill other soldiers, they must respect the rights of civilians except in dire and almost desperate extremity. Walzer's book is a passionate defense of the old principle of noncombatant immunity.

Hard cases alone can serve as tests of a moral theory. And Walzer never dodges them. Thus, in discussing aggression, he condemns preventive wars justified merely by balance of power considerations, but he vindicates the Israeli first strike of 1967. He accepts an legitimate interventions undertaken to help an oppressed people secede, or to redress, in a civil war, a balance upset by another state's intervention, or to save human lives from massacre. But even the side which resists aggression ought to keep its end moderate: Walzer condemns the American decision, in the fall of 1950, to invade North Korea in order to reunify Korea by force and he criticizes the demand that Japan surrender unconditionally in 1945 - a request that made Hiroshima possible.

In discussing the "war convention," Walzer deals with such issues as sieges and blockades, rules of engagement against guerrillas, terrorism, reprisals, mass bombings of civilian populations, and the responsibility of soldiers and officers for war crimes. His pages on terrorism are superb and uncompromising. He also discusses the moral problems raised by nuclear deterrence - a policy that consists in an immoral threat of annihilation, yet has succeeded so far in saving us from both holocaust and appeasement. But he rightly concludes that there is no moral way of fighting with such weapons: "Nuclear weapons explode the theory of just war."

Walzer's book is not merely a series of assertions and distinctions. It is also a sum of refutations. He rejects the kind of absolutism that states that, war being hell, no room is left for moral action (so that there is no escape from the dilemma: total abolition, or total submission). But he also rejects historical relativism; he shows the constancy of moral reactions over the centuries, despite enormous variations in mores and types of wars. He rejects the idea that in a just war, all means are tolerable, but also the notion that soldiers fighting for an aggressor stare are necessarily criminals.

He rejects as inadequate the old Catholic rule of double effort (the killing of civilians must not be an end, or a means to ane end, nor be disproportionate to the morally acceptable effects of the action); Walzer wants the actor to minimize the evil effects, even at risk for himself. Above all, he fights utilitarian standards (except in so far as otherwise immoral behavior can become acceptable in an extremity). He shows how rubbery such standards are, how easily they can be used to justify vast transgressions of rights - especially, I would add, in modern war, where the very nature and scope of the means often leads states to escalate the stakes. Walzer's concern is with erecting clear barriers to protect all those rights which human beings have not surrendered or lost through their own acts.

Critics will point out that Walzer's standards seem impossibly high (for instance, he rejects such excuses as the heat of the battle or superior orders in the case of war crimes, unless soldiers are actually forced to commit them: "The trigger is always part of the gun, not of th eman.") But if one accepts his fundamental principles, one cannot avoid its consequences. And Walzer avoids the two pitfalls that always threaten such exercises: he is not moralistics, because of his extraordinary sensitivity to the complexities of human behavior in battle, and to the constraints of statecraft and soldiering. Nor is he ever fuzzy. He agonizes, but for the sake of clarity. If we want to be serious about human rights, we must be serious about putting fighting well ahead of winning, and about fighting only just wars.

My only suggestion to Walzer concerns the rights of combatants. While he does not demand moral heroism from them, he constantly reminds them of their duty not to trample on the rights of noncombatants. In exchange, so to speak, he might have dismissed in less cavalier fashion that part of the "war convention" which deals with the rights of soldiers in battle, i.e., with the kinds of usable weapons; does the service of the state deprive them so sweepingly of the right to live that such rules are merely "circumstantial"?

Other critics might point out that what Walzer calls the "utilitaianism of extremity" - the possibility of overriding human rights when, at last, "after holding out for a long time," one has no alternative left if one wants to save one's political community - could turn out less stringent than he wants.

Walzer finds that British air raids on German cities met his standards only briefly - in the fall of 1940, perhaps in 1941, certanly not later, when the tide had turned. But, as Henry Kissinger used to remind his audiences, often the leaders cannot be sure about their situation. It is only later that they can assess whether it was still desperate, or allowed again for moral action; at the time the decision has to be made, things are not always clear.

Walzer's reply to such critics is likely to be that the whole point of his book is to make the leaders of free communities think harder, and resist "sliding scales" more arduously in times of uncertainty, when the temptation, of barbarism is so strong. Quite rightly, he demolishes the argument of necessity with respect to Hiroshima. As he puts it, "The more one can do, the more one has to do", as he shows, one almost always can do better. And his book does not only restore what he calls moral authority - " the capacity to evoke commonly accepted principles in persuasive ways" - in the realm of war, it also challenges social scientists and statesmen to ask a further question: Under what conditions - mental and technological - could wars again be fought as closely as possible to Walzer's standards" In other words, what are the ideological and material factors that have made these standards increasingly unreachable? Once we have identified these reasons, we will know what it is we must try to control and to eliminate, in order to bring about a world that would be politically and morally tolerable - not only are the two not in conflict, they ar not separable.

Nor is Walzer's intellectual contribution separable from his literary skill. His book requires concentration, for his analytic subtlety is formidable. But it is written with elegance and grace. Indeed, the unforced eloquence, the restrained moral indignation, the delicate irony, the passion for limits, and the quiet love of life which pervade these pages will remind many readers of that much maligned great artist, Albert Camus.Less lyrical, more powerfully argumentative, Michael Walzer deserves our respect and admiration.