THE 44-MONTH-LONG American war with Japan was immense in scope and complexity, fought on an unimaginably huge stage which reached from India to California, Australia to Alaska. Its cast of senior Allied commanders, each more or less fighting a "separate" war, was no less vast and varied: Douglas MacArthur in the Southwest Pacific and Philippines; Chester Nimitz in the north, central and western Pacific; Lord Louis Mountbatten and Joseph Stilwell in China-Burma-India; and, in the final months, Curtis LeMay and his strategic bombers in the Marianas. Its major battles on land, sea, beneath the sea and in the air were, almost without exception, vicious, prolonged and bloody. Its denouement -- atomic bombs exploding at Hiroshima and Nagasaki -- was epochal and the Allied victory, total.

About eight years ago, military historian Ronald Spector, then 33 years old, set out to tell this sprawling story in a single "popular" but authoritative volume. While pursuing his research, he taught and wrote history for a living at various academic posts, including the U.S. Army's Center for Military History in Washington, which last year published his headline- making Advice and Support: The Early Years, 1941-1960, the first volume of the Army's official history of the Vietnam War. Now a professor of history at the University of Alabama and a major in the U.S. Marine Corps Reserve, Spector was recently recalled to active duty to write an official history of President Reagan's Grenada operation.

Despite these demanding tasks, one part of Spector's mind apparently remained glued remora-like on the American war with Japan and now we have the results of this perseverance. In a word, Spector has done the impossible and done it with dazzling brilliance. Mining a warehouse of material with absolute control, Spector has produced a superbly readable, insightful, factual, gripping, unbiased one-volume history of the American-Japanese war that is, at the same time, a glorious celebration of the American spirit and (rare, these days) a ringing tribute to the American armed forces.

Everything about this book is arresting but nothing more so than its thoroughness and concision. Having been over this ground -- and water -- many times, I was sure Spector would be compelled to use intellectual sleight-of-hand to cram it all into 589 pages (counting bibliographic notes!). But I could find nothing of importance left out. Spector ranges facilely from jungle and island battlefields to the skies and oceans, where aerial dogfights and the great naval battles were fought, to high-level conference rooms where the strategy was argued out. His grasp of technical military matters is faultless but never intrusive. All the major and most of the minor battles, personality conflicts, disputations on strategy and logistical problems are woven into the fabric of his tale, each in exactly the right proportion. It's all here, but there is not one superfluous word.

The tone is likewise perfect. Spector has a well-developed sense of justice and fair play. When disputations arise -- as they do, it seems, continuously -- he lets everybody at the scene have his say, then follows with the judgment of other historians, and finally his own succinct views, which are never strident, but, rather, understated. There are no cheap shots; no axes grinding away.

The research is awesome. Spector relied to a great extent on military historians who preceded him (generously acknowledged throughout the text and notes) but on many important and controversial decisions, he has conducted research in primary sources (newly-declassified or released documents, oral histories, etc.). This new material will not make headlines but it adds significantly to our understanding of the political, military and human factors which influenced those decisions.

Skillfully interlaced into the gripping battle narrative are many convincing, controversial insights. Samples:

There is absolutely no supportable case to be made that President Roosevelt deliberately exposed the Pacific Fleet at Pearl Harbor to Japanese attack (or withheld vital intelligence) in order to propel America into the war. He dismisses John Toland's recent, weakly-documented book, Infamy, which argues the contrary.

Douglas MacArthur was "unsuited by temperament, character and judgment for the positions of high command which he occupied throughout the war." Drawing often on D. Clayton James' magisterial, but so far under-heralded, new biography of MacArthur, as opposed to William Manchester's over-heralded American Caesar, Spector has whittled MacArthur down to human dimensions, meticulously documenting the general's tactical blunders at war's outset in the Philippines and later in Papua and Leyte. Regarding the blunders in the Philippines (which, unlike Pearl Harbor, were not subjected to intensive official investigation), he writes that MacArthur "might justifiably have been relieved" of command.

The "two-pronged" counterattack strategy, wherein MacArthur advanced northwestward from New Guinea to the Philippines and Nimitz advanced westward through the central Pacific, generally accepted as a "sensible compromise," was actually seriously flawed and "might well have led to a disaster had the Japanese taken greater advantage of their opportunities." In making his case, Spector analyses two battles (Bougainville-Empress Augusta Bay and Biak) where the strategy brought America perilously close to a calamitous setback.

In order to shock Japan into a surrender and thus avoid a final bloody American invasion of the home islands, it was necessary not only to encourage Russia into the war but also to drop not one but two atomic bombs on Japan. In support of this view, Spector describes in hypnotic detail the planned invasion of Japan, Operation DOWNFALL. Owing to the expected suicidal Japanese resistance and elaborate defensive preparations and the terrain, it was estimated that the first step, OLYMPIC, an assault on Kyushu, would cost the Americans 268,000 dead and wounded. The second step, CORONET, the main assault on the island of Honshu, may well have cost America two or three times that figure in dead and wounded. Total American casualties in the two steps may well have reached (as MacArthur believed) one million or more.

Publishers say there is a continuing -- perhaps even growing -- demand for good World War II history. Remarkably (and fortunately) America has a stellar lineup of military historians who are meeting that demand: D. Clayton James, Russell F. Weigley (notably his recent, superb Eisenhower's Lieutenants), Stephen Ambrose, Charles MacDonald, Martin Blumenson, to name only a few. With The American War With Japan, Ronald Spector will surely assume a place in the very front ranks and I hope he finds time to do more.