MATTERHORN, by Karl Marlantes. Atlantic Monthly Press, 598 pp., $24.95.

The catch-22 for any author of battle-line literature is to convince the reader that he or she can't possibly understand what war is like unless they were there - and then take them there. It's a contradiction, like fighting for peace, but if there's anything debut novelist Karl Marlantes understands, it's contradiction.

After all, Marlantes served as a Marine in the Vietnam War, a conflict built on obfuscation, betrayal, thwarted principles and fuzzy objectives - sins that the decorated ex-officer grinds into every chapter of "Matterhorn," his messily epic novel of men at war that took 30 years to find publication. As the story goes, he spent three decades writing, cutting, rewriting, refining and living a postwar life before finally finding a publisher. All of which would be less interesting if Marlantes hadn't, after all this time and life experience, produced what is so pronouncedly a young man's book.

If there are any qualities that distinguish Marlantes' novel above others - beyond, say, its sturdy characterizations, unblinking attention to detail and sprinting narrative - it's the combination of immediacy and naiveté that permeates its pages, across which some very young men scramble lest they not grow old.

These include Waino Mellas, an enlistee out of the Ivy League, which makes him both officer material and a semi-oddity in a corps of draftees and "lifers." Mellas may be Marlantes' stand-in, but there are other characters of prominence, notably 2nd Lt. Ted Hawke, who - much like Mellas - has the capacity to build bridges between the disparate cliques, claques, rednecks, black-power advocates, shirkers, dopes and heroes that make up Bravo Company. What the story probably needn't have told us, but tells us very well, is that when a crew so motley gets dumped in the jungle, it's the soldier's code they follow.

Marlantes' descriptions of battle are exhilarating, but his portrait of warriors at rest is even better - the boredom, the short tempers, the jungle rot, the gangrenous feet, even the leech which, early in the book, crawls up a soldier's urethra - are all made vivid and horrifying. Less horrifying than the decisions of Bravo Company's delinquent, self-aggrandizing and alcoholic leadership, perhaps. But horrifying, nonetheless.

What's less effective are Marlantes' efforts at broadening his portraits of the men beyond the green hell in which they've found themselves. The few vignettes he creates with women, such as flashbacks to Mellas and his ex-fiance, are clumsy appendages to a story that generally clips along with rugged grace. Part of the tonal discord can be blamed on the abrupt changes in point of view: Mellas may be offering up an interior monologue in one chapter and then, all too suddenly, we're seeing things through the eyes of the redneck Cassidy or China, the not-quite-militant leader of Bravo's black contingent. Or Lt. Col. Simpson, the hard-drinking commander who sends an unfed, underequipped company on what is essentially a suicide mission, then punishes the men for their failure.

Honor and camaraderie trump good sense and self-preservation in "Matterhorn," where anyone is likely to die at any moment, or do something amazing. Marlantes, too, has his amazing moments: Sometimes the reader is simply astounded at what he's trying to get away with ("Then he tossed down his whiskey and grinned, despite the empty hole in him that the whiskey couldn't fill"). There are also moments of awkward overreaching and imprecision:

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"Hawke broke in, imitating W.C. Fields, 'My boy, you do learn fast.'

"Fitch laughed nervously.

"The conversation with Murphy had left Mellas on edge, and the W.C. Fields imitation, a form of humor he had always considered lowbrow, grated on his nerves."

The intention may be to offer a glimpse into Mellas' patrician origins, but all it does here is make him sound like a prig - something Marlantes has spent an entire novel telling us he's not.

But elsewhere, the author imagines for us a kind of exalted despair at what men are capable of doing - to each other, for each other, sometimes in spite of each other. Readers at the end of nearly 600 pages of "Matterhorn" still may not know what it's really like to be in war. But they'll know they don't want to go. Or to send anybody else.