ACTS OF WAR: The Behavior of Men in Battle. By Richard Holmes. The Free Press. 436 pp. $19.95.

SOLDIERS: A History of Men in Battle. By John Keegan and Richard Holmes. Viking/Elisabeth Sifton. 288 pp. $22.95.

THE PHENOMENON of war has been poorly served by modern historians. Many of liberal persuasion shun it because they believe, as did Alfred Vagts, the historian of militarism, that it "militarizes minds." Those who practice war, like Helmut von Moltke, chief of the Great German General Staff and architect of victories over Denmark, Austria and France in the 19th century, too often favor versions of the military past which glorify and inspire, avoiding questions which might cause doubt and lower resolve. The result, says Richard Holmes, has been a historical genre which, because of the neglec of academic historians, too often offers a choice between the knockabout, clich,e-ridden, Boys' Own adventure story and the desiccated prose of official histories.

Well, not quite. A cloud of professional disfavor certainly has shrouded military history at least since Hans Delbruck, regarded as the first modern military historian, attempted unsuccessfully to have this subject adopted as part of the history curriculum at the University of Berlin in the late 19th century. However, this has done more to reorientate military history than to stunt it -- studies of armies and navies in times of peace, their role as political and social institutions, the relationships between military leaders and their political bosses have formed part of the "War and Society" approach to the study of military history over the past decades, the premise being that how an army fights in war depends to a great extent on the relationship between the forces and their parent societies in times of peace.

Today, battle is back. The reasons for this are complex, but I suspect it results in great part from the realization that war, once believed to have been made obsolete by nuclear weapons, has now been reinstated as an option of statecraft. If this is so, then Richard Holmes reminds us vividly what we are restoring, lest we, like those French aristocrats of 1815, learn nothing and forget nothing.

Acts of War is about battle, men in battle, the sweat, filth, misery, noise, loneliness, boredom and exhilaration, desperation and heroism of battle. Courage, while not an uncommon commodity on the battlefield, is certainly a perishable one -- "A man's courage is his bank account," said Lord Moran, a surgeon on the Western Front in World War I, "and he is always spending." It is also about preparation for battle, and about the things soldiers do both on and off the battlefield, things like get drunk, desert, shoot their officers in the back and themselves in the feet, panic, fraternize with the enemy, kill prisoners, pick fights with civilians, and commit most of the deadly sins.

Von Moltke would not have approved of Holmes' book, for it demonstrates, not so much the absurdity of war, although that may be the conclusion which a fair percentage of readers choose to draw. Rather it points up the tensions between the use of battle as, in that tired Clausewitzian phrase, "the continuation of diplomacy by other means," and the chaos of conflict, the alienation experienced by many of its participants, and the sheer madness of attempting to butcher another human being, with whom one has no fundamental quarrel, for king and country. Indeed, the reasons why a man enlists -- patriotism, a cause, ideology, adventure, a desire to test his manhood -- are seldom the ones which make him perform when staring down the barrel of an enemy rifle.

Battle is an intensely personal experience which men must endure collectively if they are to endure at all. How armies persuade men to fight when every instinct tells them to flee requires a complicated mix of training, leadership, and, above all, the inculcation of intense feelings of loyalty and obligation to the group, preferably a small one unified around a mess fire. The regimental system "makes its own unique contribution to the valor of simple men," but it is not essential -- units cobbled together under pressure of combat and assigned numbers more appropriate for Swiss bank accounts than fighting forces have also demonstrated qualities of heroism and endurance to rank among the best. In all of this, ideology plays the smallest of roles, as demonstrated by the motto of the Fourth Dragoon Guards in 1914 -- "We'll do it! What is it?"

Acts of War has not left everyone rapturously happy. The complaints have been essentially two: first, by focusing upon battle as the essence of the military experience, Holmes has exaggerated its importance. Battle occupies only a minor fraction of soldiers, and of a solder's time, even in war. Battles are so brief, they touch so few people, that, in the words of military analyst Edward Luttwak, "battle is no more characteristic of war than copulation is of marriage." By focusing upon the necessarily stressful experience of battle, and the inability of front line soldiers to make the connection between the apparent lunacy of combat and the political goals of governments, the means and the ends, we lose sight of the fundamental purpose of war preparation -- the avoidance of conflict.

THE SECOND complaint is that Holmes has not been sufficiently rigorous and analytical in his discussion of discipline, leadership and combat morale. Instead, he offers a series of elegantly arranged but essentially literary impressions of combat from which we can draw few lessons.

Of course, battle is mercifully rare, and given the increasing ratio of "tail" to "teeth" in modern armies, many soldiers may never handle a rifle once they leave basic training. But battle is the event toward which armies bend their energies, and how soldiers prepare for it, how they acquit themselves under fire, is of crucial importance, not least to presidents and prime ministers for whom an army which performs inefficiently can prove almost more useless, and in certain circumstances more dangerous, than no army at all. Indeed, some critics claim that the American failure in Vietnam was essentially an institutional rather than ideological one, and sprang from the inability of the American army to build unit cohesiveness into its combat organization.

THIS GOES some way toward answering the second criticism: that Acts of War sacrifices clarity and rigor to style. Holmes has certainly not written another "How To" book -- "How to Lose 50 Pounds in the Twinkling of an Eye," "How to Become a Millionaire before the Sun Rises Tomorrow," "How to Whip a Group of Randomlyelected American Males Into an Elite Fighting Force in 90 Days, or Your Money Back." Holmes also fails in his announced task of playing midwife in the marriage of psychology and military history. But if the result reads more like Paul Fussell's The Great War and Modern Memory than Professor Norman Dixon's On the Psychology of Military Incompetence, heavy with theory and psychoanalysis, then hallelujah for that! I for one would place Acts of War on the Pentagon's required reading list.

Soldiers: A History of Men in Battle is a less ambitious book, written as an accompanying text to a BBC film. Its task is to trace the development of Western land tactics from classical times to the Falklands War, which it does with clarity and elegance, always careful to link changes in warfare to the evolution of social and political conditions. Waterloo marked the end of an era and the beginning of modern war in several ways -- it was the last European battle in which the cavalry would play a decisive role, the last before the technological revolution in musketry and artillery would transform the landscape of war from that of a crowded battlefield to a deserted, empty moonscape, it was the last fight in which the commander sitting on a horse could personally direct the battle.

These developments made battle less gregarious, made the natural inclination of men to bunch up under fire positively suicidal, made the question of morale and combat motivation more important than ever in armies which were more anonymous, decreasingly selective, increasingly bureaucratic and technical. Perhaps, as some sociologist tell us, the heroic ethic is dead in an era of "decreasing skill differentials" between soldiers and civilians. But so long as men meet in combat, so long as wars are seen as acceptable vehicles of state policy, what motivates the soldiers to fight, and fight efficiently, will remain a question of pressing importance.