JOHN KEEGAN writes about war better than almost any one in our century. He is better than those gifted masters of military history, B.H. Liddell Hart and S.L.A. Marshall. If he is not so good as Samuel Eliot Morison, it is because Keegan writes about soldiers and Morison writes about ships. The difference is that of prose and poetry, and Keegan is 4Proust in a foxhole.

In 1975 he wrote a sensationally good book, The Face of Battle. This was an elegantly researched, highly original study of three famous battles--Agincourt, Waterloo, and the Somme--which explored the "predicament" of the individual soldier: how he fought, lived, died, or went mad "at the point of maximum danger." Now a second book, Six Armies in Normandy, examines the predicament from a different angle of vision, that of men concentrated into armies--national institutions which resemble each other but which are all different because "each is also a mirror of its own society and its values, in some places and at some times an agent of national pride or a bulwark against national fears, or perhaps even the last symbol of the nation itself."

The six armies fight in a single campaign, the victorious Allied thrust into occupied Western Europe in 1944. Keegan considers in succession the American airborne troops that dropped behind the landing beaches on D-Day eve, the Canadian infantry that landed in the teeth of the German beach defenses, the English and Scottish infantry and armor that fought to open a corridor out of the beachhead, the German panzer divisions that tried to push the Allies into the sea, the Polish e,migr,e regiments fighting within the British Army, and the Free French armored units that were allowed to lead the Allies into Paris. Keegan puts his finger on the distinguishing esprit of each of these formations, displaying his incomparable knowledge of two millennia of war-making in Western society. He is senior lecturer in war studies at the Royal Military Academy at Sandhurst, and one can only envy his students.

We are, of course, on familiar ground with D-Day: we have seen all the film documentaries and read and seen Cornelius Ryan's The Longest Day. But with Keegan we are aware on almost every page of a different Normandy, part of that ancient France chronicled by Joinville and Froissart, with its chateaux and villages, its apple orchards and calvados, its abbey church at Caen built by William the Conqueror and made of the same stone as the Tower of London and Westminster Abbey. We are also aware of the kind of war that Europeans wage so ferociously. Keegan doesn't quote him, but it is the kind of war that F. Scott Fitzgerald wrote about in Tender Is the Night:

"See that little stream--we could walk to it in two minutes. It took the British a month to walk to it--a whole empire walking very slowly, dying in front and pushing forward behind. And another empire walked very slowly backward a few inches a day, leaving the dead like a million bloody rugs . . . This took religion and years of plenty and tremendous sureties and the exact relation that existed between the classes . . . You had to have a whole-souled sentimental equipment going back further than you could remember. You had to remember Christmas and postcards of the Crown Prince and his fianc,ee, and little caf,es in Valence and beer gardens in Unter den Linden and weddings at the mairie, and going to the Derby, and your grandfather's whiskers . . . Why, this was a love battle-- there was a century of middle- class love spent here."

Keegan is passionately familiar with this kind of war, in its last and most destructive manifestation, but from a distance. "I had a good war," he begins disarmingly. "(This) is not a phrase to be written, still less spoken with any complacency, breathed as it has been on clouds of bonhomie in saloon bars from one end of the Home Counties to the other during the last 30 years. But in my case it is accurate none the less: the good war not of a near-warrior at the safe end of one of the sunnier theatres of operations, but of a small boy whisked from London at the first wail of the sirens to a green and remote corner of the west of England and kept there until the echo of the last shot fired was drowned in the sighs of the world's relief in August 1945."

In that corner, the boy Keegan explored the "secret world of the English countryside" in "the last days, know it though I could not, of a thousand years of heavy-horse farming." He might never have known there was a war on at all except for the petrol rationing and the night his parents watched a glow on the horizon--Bristol burning, glanced by the "basilisk eye" of the Luftwaffe. Into this backwater arrived the Yanks, in their "magnificent, gleaming, olive-green, pressed-steel, four-wheel-drive juggernauts" and their "jeeps, caparisoned with whiplash aerials and sketchy canvas hoods which drummed with the rhythm of a cowboy's saddlebags rising and falling to the canter of his horse across the prairie." The occupants of these marvelous vehicles showered Hershey bars on the schoolboys at the side of the country lanes. "There was, I reflected as I crammed the spoil into my pockets, something going on in the west of England about which Hitler should be very worried indeed."

After this charming, very personal overture, Keegan surveys the politics and personalities that led up to the invasion --old stuff to armchair generals. Cameo sketches of Stilwell, Wedemeyer, Eisenhower, Molotov, Marshall,,Brooke, Montgomery and Rommel serve to explain some facet of grand strategy. The evolution of the top secret Allied operational plans for D-Day is lightly but expertly sketched: as all students of the war know, American zeal, British caution, and Soviet urgency combined to produce Overlord. General Sir Alan Brooke, the British chief of staff, appears as a man utterly without illusions about the Germans: "There is no doubt that they are the most wonderful soldiers," he wrote in 1940.

Keegan's treatment of the intrepid American paratroopers in the chapter titled "All-American Screaming Eagles" displays his narrative powers at their most brilliant. He first describes their equipment and training and then evaluates their tactics on D-Day. It is a surprise to recall that the parachute only came into general use in the mid-1930s. The men were nothing if not tough: "They were volunteers, boys from the wrong side of the tracks . . . who joined for adventure, had survived the nine-mile runs, 'Gimme twenty-five' (pushups) and endless 'Hubba-hubbas' ('hurry, hurry' in what the drill instructors inexplicably believed to be Hebrew) of airborne training, had jumped in practice by day and night a dozen times and were now ready to try the real thing." Billeted on the Berkshire Downs, the men of the 101st Airborne spent their free time gambling and fighting with the Tommies for the company of local girls. When the paratroopers marched out of their camps in early June, the locals knew right away they were going to the real thing and not to a rehearsal. "It got me to see them cry and take it as they did," recalled a lieutenant years later. A worried supreme commander decided to spend the last evening with these troops, and even 40 years later the sincerity of Ike's effort to communicate with the young soldiers is oddly moving:

" 'What is your job, soldier?'

" 'Ammunition bearer, sir.'

" 'Where is your home?'

" 'Pennsylvania, sir.'

" 'Did you get those shoulders working in a coal mine?'

" 'Yes, sir.'

" 'Good luck to you tonight, soldier.' "

The world will never see such an air armada again. The sight of the great fleets of C-47s in the cloudless moonlit sky was breathtaking. In all 13,000 parachutists were dropped. One of them said he felt "a long way from home." Only four men refused to jump. It took 40 seconds for each heavily burdened man to descend. "Some sticks (of parachutists) fell to their deaths because their pilots . . . had already crossed the east coast of the Cotentin, though at least one dropped close enough to the beach for most men in it to struggle ashore and hit a track through minefields and German strongpoints to dry ground--as hard a way of invading Europe as anyone found that day. Many who landed . . . drowned all the same, for the floods of the Douve and the Merderet, undetected on the aerial photographs and invisible from the flight path, stood two and three feet deep among the reeds and ripe hay of the water meadows."

Since we know the result of the battle, the degree of suspense is not high. The merit of Six Armies in Normandy lies entirely in the skill and ingenuity with which Keegan interweaves narration with analysis. As with the earlier book, it is not so much that we learn new facts, as that we look at the old facts in an entirely new way.

Keegan's relation of D-Day and the immediately following weeks is not the definitive history of that famous campaign. But his grace of style and angle of vision will rank his book among the minor classics of military history, a book to read and reread. With Thucydides, Keegan knows that "of brave men the whole earth is a tomb"; and he understands the motivation of a man like Staff Sergeant Harrison Summers of the 101st Airborne who virtually singlehandedly captured a German coastal artillery barracks on D-Day, in the process killing 141 of the enemy: "Summers, bruised and bleeding all over his body from sharp and sudden encounters with door frames and house corners --a characteristic minor wound pattern of the street-fighting soldier--collapsed exhausted by his five hours of combat. As he lit a cigarette, a witness of his extraordinary exploits asked him, 'How do you feel?'

" 'Not very good,' he answered. 'It was all kind of crazy.'"