THIS IS a very good book, but for reasons which the author did not intend. Like Theodore White's recent In Search of History, it purports to be an organized attempt to make sense of the author's experience in the great adventure and cataclysm of World War II. In this it fails; or, rather, its conclusions are commonplace. The author revisits the island battlefields of the Pacific, where, as a Marine sergeant, he fought and suffered. He sees, at his return, that his suffering, that his experience, that all our fighting on those islands may have been in vain.

The American sacrifices remain masively uncommemorated; certain of the islands now tawdrily replicate the worst of American commercial life in 1980. Okinawa is "so preposterous, that indignation is impossible. . . . The greatest of the island battlefields, more precious than Gettysburg, at first glance appears to be covered with used-car lots, junkyards, stereo shops, pinball-machine emporiums." On his return to Manila, the author is "greeted by a delegation of ten high officials, headed by a cabinet minister," preparatory to his presentation to the "beautiful Imelda Romualdez Marcos." At Peleliu the author painfully ascends Bloody Nose Ridge, to discover that only a forlorn monument, much of the commemorative inscription worn away, marks the terrible gallantry and hideous suffering of the Marines who seized it in 1944.

The author, au fond, wants to know whether he took from his shattering experience anything of value, whether anything could justify the horror, the lies about military glory, the flags, panoplies, the thousand stupidities of the officers (Manchester, in good Marine fashion, does not like officers), the strategic mistakes. What makes young men fight? -- really "fight," not just allow themselves to be conscripted and run through Fort Dix and sent up the line. Why had Manchester "jumped hospital thirty-five years ago and, in violation of orders, returned to the front and almost certain death?"

He adduces friendship as an answer. His comrades in the "Raggedy Ass Marines," a small intellignece unit -- his wiseacre, cynical buddies "had never let me down, and I couldn't do it to them." For his act of faith and friendship the author received wounds almost mortal. Because of their scars, and his memory, and his psychic baggage, he must justify what he did, and what the country did.

All this apart, Goodbye, Darkness is a compelling account -- even if a "memoir" -- of the war in the Pacific: its strategy, geography, tactics, fighting, its leaders and even its military sociology. Perhaps no other living writer could have gotten it all down so well; but none has looked it over from so many merging or intersecting perspectives: biographer and historian of its grandest strategist, participant as Marine grunt who went to Parris Island not only because of his father, who had fought with the Fifth Marines in the Argonne, in World War I, but also because, like hundreds of thousands before and after him, he "wanted to surrender my individuality, curbing my neck beneath the yoke of petty tyranny. . . . I . . . yearned for . . . discipline."

He got a lot of it; too much. The Marines sent him to Quantico, where ambitious enlisted men with a little college were trained to be officers. But these Marines turned out to be only "upper-middle-class snobs, nakedly ambitious conservative conformists, eager to claw their way to the top. . . . Some were already learning to fieldstrip Sam Browne belts."

There follow vivid accounts of the campaigns for Guadalcanal, Tarawa, Saipan and Tinian, Guam, Peleliu, Iwo Jima, and Okinawa -- gory, in no way understated, movingly rendered and authentic. Not least of their excellence is that they explain what is going on above squad level, so that the accounts present unusual coherence. Most "military writers" have neither the wit, tact, nor interest to do this: there is the general in his tent, and the private in his hole. They seem to have little to do with each other. Less convincing are the interstitial descriptions of Manchester's pilgrimages to these now desolte or exploited places, his attempts to find . . . exorcise . . . well, we are not wholly certain.

Goodbye, Darkness is called a memoir, not an autobiography. As a memoir, it succeeds superlatively -- the author somewhat detached, stitching together his recollections of what men did and suffered, allowing the evidence, the tales, the descriptions of men and terrain to evoke the isolated past of infantry fighting in the Pacific, a past almost as surely closed from view as the Japanese caves on the islands defied penetration by naval bombardment. As self-conscious autobiography, as an attempt to make sense of the war and his part in it, given the author's and the world's state 35 years later, it is much less accomplished, doomed in the telling by questions ultimately unanswerable.