When policeman-turned-novelist Bill Caunitz makes a rare visit to his old precinct post, the One-Oh-Eight in Queens, N.Y., the star treatment he gets makes him uneasy. Plainclothes cops who look like the scruffy "hair-bags" that populate his books greet the ex-detective as if he were a Beverly Hills cop with a three-picture deal.

"Hey, Lou!" a pot-bellied lawman bellows, using standard cop shorthand for lieutenant. "Saw ya on Donahue." A narc in a Hawaiian shirt claps Caunitz on the back. "When's the movie coming out, Lou? They gonna make it a series?" Retreating upstairs to the squad room of the Anti-Crime Unit, which he once commanded, Caunitz grabs a Styrofoam cup of muddy station-house coffee and pulls up a chair. "I like anonymity," says Caunitz, gray and balding at 52. "I wanna be one of life's character actors."

When a detective tells his former boss that he plans to retire after 20 years, Caunitz, a 29-year man himself, bluntly advises against it. "There's nothin' out there," he says. "If it wasn't for the books, I'd be here too. This is still the greatest job in the world."

Caunitz' enthusiasm for what cops across the country call simply The Job has helped put Suspects (Crown, $17.95), his second novel about the secret life of policemen, on the New York Times best-seller list. The book's success is proof that Caunitz' 1984 blockbuster first novel, One Police Plaza (1.3 million paperback copies sold), was no fluke. While noting that the prose in Suspects is "sometimes stilted," the Times applauded Caunitz for creating "palpable excitement" and making "this arcane blue world come alive."

Suspects, like Plaza, is an action thriller that appeals to the public's seemingly insatiable lust for police lore and gore. It may be simple civilian curiosity to learn about the boys in blue. Or it may be Caunitz' word-picture close-ups of shotgun slayings and police orgies that are hooking readers. Caunitz isn't sure himself. "I know about cops; I write about cops," he says. "And people love it. Women, who buy 65 percent of the books in this country, like learning about men. And the cop world is, after all, a man's world."

Cagney and Lacey might differ. But then, they wouldn't be admitted to the departmental stag parties-cum-live-sex shows that Caunitz' crapshooting, six-pack-guzzling cops occasionally stage. Caunitz' men in blue do not sport creased uniforms and spit-shine demeanors. Plot lines entwine murderous rogue cops, police groupies and Mafia capos. Caunitz insists his fiction reflects the realities of The Job.

Retired for two years, Caunitz still has the Right Gruff, an attitudinal mix of weary cynicism and moral outrage common to many policemen. It's a perspective built on haunting memories that Caunitz weaves into his fiction. A partner who was shotgunned to death "on a nothing assignment" became a murder victim in Suspects. The horrifying curtain-rod murder that opens Plaza is based on two homicide cases Caunitz worked on. Some cases, such as one in which a mother helped her boyfriend rape her 12-year-old daughter, are, he says, too gruesome for fiction.

"Those are the kind that eat your intestines out," he says. "That's the part of police work that makes you hard. You learn not to trust people. You learn that just because someone is dressed in a nun's habit doesn't mean they can't pull out a gun and kill you."

All policemen tell "war stories." Few have made a career out of it. Caunitz says he was drunk and "running off at the mouth" at a cocktail party in 1974 when Harcourt Brace's late co-publisher Tony Godwin told him to write his stories down. Caunitz, whose 25-year marriage ended in 1978, was living alone at the time, and the next day, while nursing a hangover, he set to work on a spy novel. Weeks later he mailed a few chapters to Godwin only to get a damning two-page critique in return. Caunitz decided to "forget about being a writer" until he read the last two lines Godwin had typed: "Despite the above, I think you have a little talent. Stay with it."

Through 10 years and a succession of editors and agents who ordered countless rewrites, Caunitz stuck with it. He wrote during the day and worked the midnight-to-dawn prostitution detail out of the One-Oh-Eight. "I don't know how the hell I did it," he says.

The son of a professional piano player and a housewife, Brooklyn-born Caunitz says he "wandered into" police work following a stint in the Army and a dull insurance job. Joining the NYPD in 1955, Caunitz was assigned to a foot patrol. "I'd walk the street, twirling my baton. I'd hit myself in the head and look around to make sure no one saw." Back then Caunitz expected he'd "retire to Florida with all the other old cops." Instead, he's living in a recently purchased Manhattan co-op.

Two years ago, with $385,000 for the paperback rights to Plaza already in the bank, Caunitz was on a Queens rooftop wrestling with a robbery suspect. "I'm rolling around," he says with some disbelief, "and I remember thinking to myself, 'What the hell are you doin'? You're too old for this.' " It was then he realized that maybe he had stayed on The Job a little too long.

Now at work on his third cop novel, Caunitz says he's had no second thoughts about quitting. "Writing is as exciting as police work, if not more. The Job can get monotonous. It's not all bang-bang, shoot 'em up." Though it may not be "the greatest job in the world," writing has its moments. "Watching my characters come alive on the screen [in a made-for-TV version of Plaza due this month] was a wonderful ego trip. And when I read something I have written, I think, 'Wow, that came out of my brain!' It's a great feeling."