Philip Caputo pierced many war-hardened hearts with his 1978 autobiography, ''A Rumor of War'' (Ballantine, $2.50 in paperback). Like a Vietnam diary never intended for unfamiliar eyes, it is humble, honest, and revealing. Every line is credible, every raw feeling utterly human. With poetic tenderness Mr. Caputo illustrates the prosaic reality of men in war. He is anyone's son.
Though patterned after the author, the hero of Mr. Caputo's recent novel, Del Corso's Gallery (Holt, Rinehart & Winston, $15.45), is unfortunately unrecognizable.
Nick Del Corso, a war photojournalist, is a first-generation Italian-American eager to enter society's mainstream but never believing he is flowing with the current. Possessed by his passions, Nick's ambitions become ''terminal,'' his loyalties a ''personal mission'' gone amok, and his Roman Catholic superego a self-impaling petard. In perpetual motion, compelled by all but unrelenting guilt with periods of atonement, Nick bludgeons life with such intensity that he is a disaster waiting to happen.
It does, when Nick, an Army photographer in Vietnam in 1965, passively witnesses with his camera a My-Lai-type massacre at Rach Giang. Emotionally detached, he has soldiers place corpses in a more aesthetic arrangement for his camera, recreating Goya's ''Disasters of War.'' The resultant pictures - Del Corso's Gallery - which constitute prima facie evidence of his sins of omission and commission, are entombed in his files, along with Nick's capacity for joy and peace.
Never resolving his inability to act, he never mourns and thus never feels he is absolved. Instead, he sublimates his helplessness by becoming the personification of his camera lens, a man no more morally accountable than his Leica.
With this destructive, unre-solved ethos, it is little wonder Nick cannot adjust to civilian life. He rejects the safety and comfort of family life and commercial photography and seeks high danger in an obsessive search for absolution.
He returns to Vietnam and encounters his former mentor and alter ego, P. X. Dunlop, a Pulitzer-winning photojournalist who feels as compelled to airbrush war's ugliness - exploiting only its heroics - as Nick does to magnify its every human weakness and atrocity. Each religiously committed to his personal view and vying for the same professional and emotional prizes, they are bound together in a suicidal zero-sum game.
Thus, Dunlop reports the war with a long-lens remoteness, helping civilization ''defend itself against its enemies'' by expressing its best values , even ''in the midst of war's degradation.''
Nick focuses on the degradation, following World War II photographer Robert Capa's law: If it isn't close, it isn't true. By disturbing people with Goyaesque grotesqueries, Nick would ''make the powerful pause and reflect before they act out their napalm fantasies.''
His ''purpose'' - the rationale of Nick's credo - grows into a ''personal mission,'' protected by his gods yet possessed by inflexible deamons.
Repeatedly, Nick is offered, redemption, split-second opportunities to save lives - and in the process, perhaps, himself - if only he will forego his chance at the Pulitzer and act apart from his camera. Yet he cannot. When his pursuit for the perfect angle contributes to a friend's death, he feels the first of his guardian gods desert him.
Nick and Dunlop evacuate from Vietnam with the last helicopters in 1975, their personal war intact. Their new arena is Beirut, but Lebanon proves a different kind of war.
There is none of Dunlop's treasured war heroics, none of the ugliness that could make a difference for Nick, just brutal slaughter, serving no apparent purpose but senseless revenge. Both men face despair. Doubting himself openly for the first time, Dunlop wonders aloud: ''Maybe all photographers were accomplices to an extent.''
Yet war becomes an addictive movable feast for photojournalists, and the same cast that sat around the Caravelle in Saigon surfaces in the poshest of Beirut's remaining bars.
One of Nick's friends, Harry Bolton, a professional whose last journalistic illusions are dissolved in the Lebanese blood bath, strips Nick of any shred of self-deception: ''You want to make (Americans) feel responsible, the way you do. . . . I don't think you want to make them see. You want to make them pay.''
Nick realizes too late that in trying to pay his original debt at Rach Giang, he has incurred many others. By his senseless death, Nick is denied what he hounded in life - a purpose.
In the sense that Caputo wrote about what he knew, ''Del Corso's Gallery'' is authentic. Yet, the personal flavor of Vietnam is mysteriously missing. Instead, ''Del Corso's Gallery'' seems novel-writing-by-headline - familiar events and stereotypes strung together as a plot.
''Del Corso's Gallery'' is to war fiction what Robert Ludlum's books are to spy literature: an evening's escape. Yet plowing through the labyrinths of Nick's psyche is exhausting, and, by the end, Nick's eddying intensity has long since drained the reader's capacity to care. We are relieved his torment - and ours - is over.