Formed and Deformed by War : SLOW WALK IN A SAD RAIN By John P. McAfee ; (Warner Books: $18.95; 256 pp.)

This novel is booby-trapped. About halfway into it, former Special Forces Capt. John P. McAfee pulls the pin on a grenade and leaves it in our path through the jungles of Vietnam and Laos. We watch him do this. Yet McAfee is a skillful enough writer to make us forget we saw. He distracts us with cobras, leeches, narrow escapes, double crosses and a hundred gruesome varieties of death until, with the story seemingly over, the grenade goes off.

The result is a book you’ll remember for a while after you close the covers. The trouble is that it isn’t easy getting to the point where McAfee sets the trap. Two reasons for this (in the terse, staccato paragraphs he favors):

Absurdity.

And attitude.

The absurdist--as opposed to heroic--treatment of war in literature dates back at least to Fabrizio’s surreal vision of Waterloo in Stendhal’s “The Charterhouse of Parma” and Pierre’s muddled impressions of Borodino in “War and Peace.” It reached maturity in “Catch-22.” And certain nasty peculiarities of the Vietnam War made this approach--once so radical and shocking--the preferred, even the only way to write seriously about that conflict.

Besides, it’s convenient. Ex-hawks and ex-doves can find a Big Hootch to share there, if nowhere else. Whether they feel that the United States shouldn’t have fought in Vietnam at all or that we should have nuked the North back into the Bamboo Age, writers and readers can agree: Yes, this war was one weird, twisted nightmare.

There’s a drawback to this kind of consensus, though. McAfee says most of the things he writes about really happened, but he makes them all happen in the space of a few months to a single Green Beret “A Team” stationed in the Mekong Delta. Craziness and carnage come so thick and fast that “Slow Walk” seems to refer as much to other Vietnam novels as to life.

The characters, too, seem awfully literary. Specialist Thompson, the team’s electronics whiz, is “that pimply-faced teen-ager who invites you up to his room to show you how he’s wired the door with a 60,000-volt current to kill his parents.” Quiet Voice, the medic, speaks only in questions. Spaghetti, a black from Harlem, speaks only in Senegalese proverbs. Shotgun, the team’s senior noncom, is both an indispensable source of survival skills and a homicidal maniac whose favorite targets are U.S. Army colonels.

Which brings us to attitude.These are angry people. Their anger isn’t directed at the North Vietnamese--”the other team” in a game whose rules are “1. Stay on your side of the 50-yard line. 2. You cannot play offense. 3. You cannot score”--but at the politicians who made the rules, the brass who order them out on stupid missions, and anybody else who hasn’t had the same gut-wrenching experience, who isn’t a Green Beret.

This anger, and the black humor that expresses it--”Slow Walk” is nothing more than a long string of wisecracks--is absolutely authentic. Still, it puts us off. This isn’t the kind of war novel in which innocent youths are hardened into soldiers. These soldiers show no traces of their former lives. They are a gung-ho elite, a collection of macho poses with nothing human peeking through; their only regret seems to be that they aren’t in a better war.

“There was a time I liked being a soldier,” Shotgun says. “It was bloody, sure, but it meant something. Now we’re just janitors. Some damn politician or colonel makes a mess and we get to sweep it under the rug.”

Then something happens. We discover that this same Shotgun is a closet humanitarian who sends half his salary to a Bolivian orphanage, warning the priests in charge not to educate the children too much. “When I was a young private in WWII,” he writes, “I was impressed with the minds behind the (Nazis’) weapons. . . . Then we found those camps. . . . I want you to teach them to be human beings first.”

And it’s Shotgun who helps set the booby trap by refusing, for the first time in his career, to obey an order. The Green Berets are on a secret mission deep in Laos. They have stumbled across a 4-year-old boy and his grandfather herding cows.

Take them along and they’ll make too much noise.

Leave them behind and they’ll tell somebody.

The decision is up to the narrator--a young captain, just as McAfee was.

The mission, as it turns out, was designed to fail. The A Team discovers what it wasn’t supposed to--that Hmong tribesmen are growing opium and the CIA is smuggling it on a huge scale, with North Vietnamese connivance. Drug sales are funding arms purchases by both sides in the war. After that, the team’s deadliest enemy isn’t the communists any longer but “Hawaiian shirts” flying unmarked helicopters with guns “that could put a bullet in every inch of a football field in one minute.”

Still, the captain could have faced that same decision on the soundest of missions, in the best of wars. It has nothing to do with Vietnam. Or the absurd. He flees from this knowledge, as do we, into a final orgy of cartoon mayhem and paranoia that features giant snakes, rampaging elephants, Phoenix Project assassins, old French tiger cages and--just as a sideshow--the Nixon-Kissinger invasion of Cambodia.

Then the narrator goes home.

The grenade explodes.

And we discover that, underneath all the hard-boiled, high-tech, movie-script stuff, McAfee has turned the standard war novel upside down. This isn’t a story about losing your humanity in combat; it’s about finding a shaky, tortured kind of humanity afterward--if you’re lucky. Maybe, he implies, humanity doesn’t even mean anything until you’ve faced the worst that human beings--including yourself--can do.

“Maybe,” the narrator says in wan hope, “the mind that looks back and judges is a more mature mind than the one that made the decision in the first place.”

The anger, though, never goes away.