LAST SUMMER, a soft-voiced middle-aged man with haunted eyes approached me at a backyard party. He knew I'd created Rambo, and he wanted to talk. What about? I asked. What he'd done in Vietnam, he answered. We took a stroll, and with a calmness that didn't hide his distress, he described his experience in the war. The next night, he phoned me from the psychiatric ward of the local veteran's hospital, where he'd just admitted himself. "It helped to talk," he said. "To get some of my nightmares into the open. Lately I've been having urges to kill myself. I can't stand the guilt." His treatment proved successful. A psychiatrist helped him adjust to his nightmarish past, partly by reassuring him that guilt was a natural reaction to the terrible things the war forced him to do.

Not all Vietnam veterans have suffered such severe and long-lasting effects from the war, of course. Soldiers who served in conventional units (if anything about Vietnam can be described as conventional) have by and large adjusted to civilian life. But the small percentage of soldiers involved in Special Operations endured extremes of training and combat that often left psychic scars. One of the most harrowing of these Special Operations -- and the cause of my acquaintance's nightmares -- was the Phoenix program or the Blackened Bird, the subject of Nicholas Proffitt's new novel, The Embassy House.

As Proffitt describes it, the rationale for the Phoenix program was "to beat the VC at their own game." The tactics were "simple: quick raids into Viet Cong hamlets, random torture of villagers to gain intelligence, swift execution of identified VC leaders." Organized by the CIA, supervised by elite American soldiers, carried out by South Vietnamese troops, the program eventually got out of control, however. The units who took part in it often degenerated into hit squads. "The CIA put head prices on targets and turned its back on looting. The spooks' cavalier attitude toward the rules gave . . . the impression there were none, and the excesses grew. Instead of bringing in VCI suspects, the South Vietnamese troops began to shake them down. If they paid, they lived; if not, they died on the spot." Either that, or Phoenix enforcers "went for a scattershot approach, picking up anyone who might be a suspect. And when the jails were filled to overflowing, they began taking the law, such as it was, into their own hands."

So far as I know, this subject has never been the focus of any of the myriad novels that concern themselves with Vietnam. As if to emphasize the book's fresh topic (in a subgenre that frequently seems repetitive), the "embassy house" of Proffitt's title refers to one of the compounds from which the CIA directed Phoenix operations throughout Vietnam. The novel's main character, Captain Jake Gulliver, a skilled Special Forces assassin whose code name is The Sandman and whom the enemy calls The One Who Comes at Night, is reassigned to the CIA at the embassy house, and there, despite his years of cold detachment, he can no longer tolerate what he does and is a part of. Gulliver's antagonist is Bennett Steelman, a ruthless CIA section chief with the code name Razor, for whom facts are a way to hide the truth and ethics are subordinate to expediency. When an innocent Vietnamese is mistaken for a Viet Cong operative, tortured by Phoenix personnel and murdered, Gulliver reacts with long-suppressed outrage. As local villagers demonstrate their own indignation, only to be attacked by supposedly friendly soldiers, Gulliver's quest for justice leads him to a violent confrontation with Steelman in the eerie Plain of Reeds.

HE PLOT of the book is more complicated than this summary indicates, with strong supporting characters (in particular Gulliver's Vietnamese mistress and a Vietnamese soldier who is Gulliver's sole male friend), as well as twists and betrayals that I don't want to give away. But it won't ruin the reader's enjoyment of the story if I point out that Proffitt, whose previous book Gardens of Stone recalled war fiction by James Jones and Norman Mailer, writes knowledgeably about his subject. He was a sergeant in the U.S. Army and later, as an award-winning journalist, covered the fall of Saigon. His authentic details make the reader believe that this is what South Vietnam was like in 1970.

As one might expect from a war novel in which characters are codenamed The Sandman and Razor, there are elements (in a good sense) of a thriller here. Perhaps because of that, quiet scenes seem overextended in comparison with scenes of action. Another quibble: when characters think to themselves, they often do so in cliche's (something was as hard to do as pissing into a typhoon, or so-in-so had to be terminated with you-know-what kind of prejudice). These expressions are no doubt true to the personalities of some of the characters but are nonetheless overly familiar.

Still, these reservations don't distract from the force of Proffitt's narrative. He writes extremely well about combat. His sense of place is evocative. His analysis of politics in South Vietnam is fascinating. The last 70 pages are especially fast and suspenseful. The Embassy House stays in mind after its covers are closed, and in a subgenre that I thought had exhausted itself, that's impressive. I plan to send a copy to a friend who's working on a Vietnam novel -- to warn him about the competition.