‘A Tunnel at the End of the Light’ : FLOAT, <i> By David Eyre (Doubleday: $19.95; 393 pp.)</i>

In 1991 it still feels appropriate to write a novel about the Vietnam War in present tense. In present tense, novelists create the impression that an event remains unfinished. For the generation now entrenched in middle age, Vietnam does not go away. We sift its ashes in search of our souls’ ease. Yet only one writer, Tim O’Brien, has written of Vietnam with a power and artistry equal to David Eyre’s in this astonishingly impressive first novel.

If O’Brien is Vietnam’s Norman Mailer, David Eyre is, as “Float’s” jacket flap promises, its Joseph Heller. Unlike the grim intensity of O’Brien, Eyre’s sardonic wit suggests his having gained more distance from the war. Thus, “Float” feels less viscerally immediate than O’Brien’s National Book Award-winning “Going After Cacciato” or National Book Critic Circle Award finalist “The Things They Carried.” Some may wish Eyre had written a different book, but few could hope for a better one.

Back when the White House still has its hymnals turned to “What a Friend We Have in Saigon,” John Paul Dubecheck, a 24-year-old former Washington State University football player, is a “Special Warfare” naval lieutenant (junior grade) combing the Mekong River Delta although he’s never sure who the enemy is: “I wish there were front lines and rear lines and you knew where in the hell you were and who the hell to kill and maim and cripple.” In Vietnam four months, Dubecheck already finds his comrades “more important to him than his mother.”

The whimsical cast of this picaresque novel include Lt. Cmdr. C. B. Foote, a.k.a. Tuta, the maudlin officer who collects Hieronymus Bosch, and Norman Dupree, the “nearly normal” intelligence officer to whom Dubecheck laments that there will always be war even if only one nation wants it: “War’s sorta like golf, you can play it by yourself.” There’s Dubcheck’s homicidal roommate, Michael Recore, and Anastasion, the civilian American nurse who solves any problem by dispensing a shot of morphine: “If God didn’t want us to have morphine He wouldn’t have given us veins.”

Eyre, whose writing background consists thus far of screenplays (most recently the 1989 television movie “Everybody’s Baby: The Rescue of Jessica McClure”), was himself a naval officer in Southeast Asia in the 1960s. He moves Dubecheck less through a linear plot than a series of dazzling episodes that would translate brilliantly to the screen. In one, Dubecheck finds a drunken chaplain at a party. “You oughtta bring Christ into your life or, if you’d rather, have another drink. Six o’ one, half dozen of the other,” the chaplain counsels, then drives our hero into enemy territory in search of a liquor store, shouting “PurraiseJesus!” all the way.

Appealingly irreverent (what can they do to him, he figures, send him to Vietnam?), Dubecheck is unrattled by Anastasion’s dire prediction of his fate. “Will I be okay?” he asks.

“No way. You’re gonna die.”

“Yeah, well, not in my lifetime.”

In the States, the nuances and absurdities grow thicker. Dubecheck is a floating man from a directionless war back in a nation that thinks it knows where it’s going but may be most lost of all--symbolized by “Drifting Cloud,” a Mexican from San Pedro passing himself off as a Sioux. Dubecheck meets a hippie, Jane, who calls herself Lulu, and shares a vividly described acid trip.

The perils of America--ominous muggers, brutal U.S. marshals--can’t frighten a man who’s seen the Mekong, but they do make him run back to Vietnam, “that dreadful place that feels more like home than home,” for the darkly comic conclusion: a spectacular fake skirmish staged for visiting Phil Kealy of the House Armed Services Committee, a “no-nonsense congressman,” which means “he starts drinking at five in the afternoon instead of four.”

Set among hilarious scenes are images of searing pain, the nightmarish reality of war and riveting tension right to the end; GIs tauntingly molest Vietnamese women, decaying corpses float in rivers and “Crispy Critters” lie scorched in fields, babies with shrapnel in their backs bleed to death while inches away schoolgirls have turned whore, mothers wade among the scattered organs of their bombed 5-year-olds.

All the while, in what must rank among the best first novels in a generation, Dubecheck seeks to learn who he is. The drunken chaplain already has told him: “A Christian soldier. Damndest oxymoron I ever heard.” Growing resigned that probably “there’s just a tunnel at the end of this light,” Dubecheck tries at least to appreciate the light.