The Killing Aristocracy of the Green Berets : SYMPATHY FOR THE DEVIL<i> by Kent Anderson (Doubleday: $16.95; 350 pp.) </i>

From the author’s own darkness, from the nihilism once necessary to his own military function, comes this ugly yet holding chronicle keyed to a subtle unglory of the Vietnam War: the caste system, by combat specialty, not rank, of the U.S. Army.

Its aristocracy wore Green Berets, followed a code beyond any convention of West Point or Geneva, fought brutally, and, of critical importance to their status, volunteered to risk as they did.

The commoners were youngsters arriving in-country as ill-trained fodder and foul-ups; unwitting, unwilling draftees hiding behind bravado and surviving by long odds or rear-area postings.

They could not understand each other. They did not want to. Their division did not even change the outcome of the war. It simply was one more writhing within an incredible screw-up that slowly is clearing its path through the American conscience.

Kent Anderson, as a former Green Beret sergeant, writes hugely and precisely of what he knows best, the men and mentality of the Special Forces and their cross-border operations. His principals, Hanson, Quinn and Silver, kill as easily as they drink, but cognac produces the greater remorse and need for apology.

They are not psychotics. They simply are suited by a lack of civilian direction, by a primal talent for survival of the vicious, by the challenge of their own insecurities and physical limits, to be superb warriors. The system knows it, seeks them out and makes them Green Berets.

Hanson enjoys The Threat of the spit-shined jump boots, the swagger and starched fatigues: “He liked it that people stayed out of your way, gave you room. He liked the way it simplified arguments, the way The Threat said, You may be right in your argument, it’s an interesting idea and I’ve enjoyed talking to you, but I can still kick your ass anytime I want to.”

He accepts the seduction: “It is not possible to soldier with an army’s free men and best killers without becoming one of them.”

He uses the fatalism that exorcises fear: “If you win, the other guy’s dead. Period. And you’re alive. If you lost, you’re dead, and your problems are over.”

His drugs are government issue: “ ‘Special Forces popcorn, gentlemen, dexamphetamine. It makes you mean. It makes you want to go out and kill Charles with a knife, with your hands and teeth. It makes you want to go out and have fun with Charles.’ ”

And Hanson becomes an animal: “Sixth sense is only the other five senses fine-tuned to threat. A shift in the rhythm of the silence that opens your eyes. A shudder in the pattern of shadow. The hint of some smell that brings your head up . . . a group of men moving through the dark with plans to kill you gives off an energy you can feel.”

Elitism, however, is intolerant. The team’s superiority becomes overriding, destructive. Army discipline is replaced by the Green Beret system. Foe is more respected than friend, and the military mission is subjugated by team loyalty, the ultimate morality, men believing in themselves and nothing else.

In the end, there are no good guys, just guys who measure up and guys who fall short.

The final chapter is based on that thought and the reading is explosive. It even makes grisly sense. So does Hanson’s realization that no matter his acts, no matter the number of dead, he is doomed to survive the war. And the nightmares will be about home.

Anderson has a profundity found only with novelists of the human experience who have observed, can interpret and then carry us back to smell, hear and bleed.

In his craftsmanship, there’s every promise that its power will easily transfer to works of peace.