The reviewer writes for Editorial Research Reports.

Psycho killer on the loose? Round up the usual suspects, Vietnam veterans. That was the theme played out in too many movies and TV cop shows a few years ago before Hollywood got the message that stereotyping the Vietnam vet as a crazed killer is akin to portraying a black man as lazy and shuffling. That was before the word had sunk in that of the 2.7 million men and women who served in Vietnam, the vast majority have adjusted well to life back home.

"The Park Is Mine" and "The Ultimate Good Luck" are novels in which the main character is a Vietnam vet whose war experiences color his life. The portrayals of the two men, though, are vastly different. Harris, the anti-hero of Stephen Peters' first novel, would fit perfectly in any "Kojak" episode. He's a war-damaged maniac who carries on a one-man crusade of violence. Richard Ford's hero, Harry Quinn, is a troubled nomad in search of love and peace of mind. Harris is stuck in a mediocre thriller; Quinn pulsates through a top-rate novel.

Harris' violent craziness makes for quite painful reading. He terrorizes New York City for six days by single-handedly taking over Central Park. In destroying the cops who try to flush him out, Harris employs nearly the entire catalogue of booby traps, mines and other deadly guerrilla weaponry used in Vietnam. He pops amphetamines to stay awake and goes on patrol at night.

This is another reason "The Park Is Mine" makes for painful reading. It is badly written. The book is filled with dull, dense writing, much of it in the passive voice, much of it bogged down in tedious descriptions. This is supposed to be an action thriller. But Peters, whose background is in television production, has produced a book that seems barely more than the plot outline of a made-for-TV movie. His descriptions of the park's undergrowth, rocks, lakes, walkways and meadows cry out for camera work. His writing cries out for editing.

The book fails on another important count: Much of the plot is not even remotely plausible. Part of the fun of a good thriller is the possibility that the author has hit on an idea that just might happen. But it's hard to picture anyone getting away with what Harris goes through to set up his big terrorist scene. Harris spends weeks schlepping tons of barbed wire, claymore mines, machine guns, ammunition, food and even a motorcycle into the park. Anyone preparing for World War III right in the middle of town could not possibly go unnoticed -- not even in New York City. And Harris' superhuman six-day victory against New York's finest SWAT teams defies logic.

But Peters' worst sin is his shameful use of a demented Vietnam vet as his central character. What compounds the situation is that Peters -- who is not a Vietnam veteran -- provides evidence that he knows the violent vet is just a stereotype. He has a psychiatrist say, "Only in the rarest of circumstances does this delayed stress compulsion result in violence . . . Most vets have handled their problems."

That Peters knows the truth, yet still produces a novel -- with a big paperback sale, a movie deal, tons of publicity and an excerpt in Penthouse -- with a stereotype of the war-crazed Vietnam veteran, is unforgivable.

Harry Quinn, the main character of Richard Ford's second novel, "The Ultimate Good Luck," is no stereotype. He is too complex to fit any easy category. A drifter, a survivor, he is a good man to have around in a crisis. But he's not likely to stay in one place too long. He constantly analyzes life's complexities, but never comes up with any lasting answers.

Ford -- a former Marine who did not serve in Vietnam -- has written a novel that succeeds in each area where Peters' fails. The plot is thoroughly believable without being trite or unimaginative. Ford's storytelling works well; his use of flashbacks gives insight into the characters' makeup without ruining the story's flow. The dialogue rings true in a jangled, offbeat way. In this scene, for example, Quinn and his girlfriend Rae are about to split up:

" 'I don't know what you expect me to do,' she said.

" 'Nothing,' he said. 'Anything.' He began to eat his eggs.

" 'But can you please just tell me what it is you don't like or do like. I feel by myself even when you are here anymore.'

"He looked up at her across the table. 'I don't know what I can do about that,' he said. 'You can be by yourself with me.'

" 'And is that good enough for you?' she said.

" 'I guess so,' he said.

" 'But what?'

" 'But nothing.' He put his fork down and wiped his mouth.

" 'Is that all?' she said.

" 'I'm alone most of the time,' he said."

"The Ultimate Good Luck" is set in and around Oaxaca, Mexico, where Quinn journeys to get Rae's dissolute brother out of jail. Quinn's ordeal calls to mind the misadventures of Ray Hicks, the hero of Robert Stone's powerful novel, "Dog Soldiers." In both books, a Vietnam veteran tries to help an amateur drug dealer in trouble with the big boys. Unsavory characters abound; there is plenty of violence.

Ford's story, like "Dog Soldiers," casts a spell of chilling eeriness. Part of this is because of Ford's depiction of Oaxaca as a nervous, murky city with terrorists on the loose and the police shooting first and asking questions later. The exotic, nearly impenetrable Oaxaca is a fitting backdrop for Ford's tale.