THE STRAIGHT MAN <i> by Roger L. Simon (Villard: $15.95; 225 pp.)</i>

The private detective of fiction who suffers from either a physical or mental ailment, real or imagined, is not exactly a fresh conceit. A raft or two of them can be recalled, if dimly, without too much effort.

Some of fiction’s impaired private detectives have been minus an arm or a leg. One or two have been blind. Several have been fat, even obese. Far, far too many have been alcoholics or recreational dopers. And others have just seemed to miss their mommies. Or daddies.

The disability, whatever its nature, is useful to the author because it provides yet another obstacle the detective must leap, stumble or crawl over. It also lends a bit of verisimilitude, if not much character, and seemingly helps avoid the steely-eyed, iron-jawed stereotype.

A clever and gifted writer can, of course, seize a stereotype, turn it around or even inside out, and produce an amusing and witty variation on an all too familiar theme. Fortunately, Roger L. Simon is a clever and gifted writer.

Simon’s private detective hero, the engaging and insouciant Moses Wine, is a refugee of sorts, still fleeing the political ravages of the ‘60s. When last seen in Simon’s fourth novel, “California Roll,” Wine was settling into a cushy job as chief of security at a Silicon Valley computer firm.

But in “The Straight Man” he has quit that job and is back in West Los Angeles, half-heartedly plying his private detective trade out of his apartment, and trying to cure some vague and ill-defined Angst by thrice-weekly visits to a psychiatrist with offices in Santa Monica canyon.

Before a lip can be curled at a private eye who would resort to psychiatric help for depression, rather than the standard fifth of Jack Daniel’s, Simon tosses in his first plot twist. The psychiatrist, who is himself crippled and confined to a wheelchair, asks Wine to take on the investigation of a possible murder.

It’s one of those did-he-jump-or-was-he-pushed cases. The dead man, Mike Ptak, was the husband of a woman the psychiatrist is treating. Ptak was also the straight man and white half of a famous black and white comedy team that recently split up. The widow is convinced her husband did not commit suicide. She is less sure that his former black partner, Otis Pike, isn’t responsible for his death.

Otis Pike, it turns out, is none too well wrapped either. Wine locates him in the Malibu Colony under the around-the-clock care of yet another psychiatrist who has all the earmarks of a charlatan. A drug- and booze-ridden wild man, Pike is trying to get himself sane and clean enough to fulfill the multimillion-dollar movie contract he has recently signed. As for his ex-partner, Pike feels only contempt, dead or alive.

With what the seasoned reader will recognize as several prime suspects already in view, Wine plunges into his investigation not only for the money, but also as a kind of occupational therapy. It takes him all over Los Angeles, which Simon describes in fresh and cunning detail, and to New York where the plot is seasoned with King King, Otis Pike’s brother and putative emperor of the dope trade.

There are also some evil Koreans; a scam involving Bibles for Bucharest, and a refreshing new assistant for Wine in Chanta Barrault, a pretty French-Canadian and failed stand-up comic, whose secret longing is to be a private detective. Also back is Wine’s septuagenarian Aunt Sonya, the irrepressible and unreconstructed Trotskyite. And as usual, there are enough dead bodies to keep things lively.

Simon has a fine ear for dialogue and an equally fine eye for telling detail.

This may be the best of the recent adventures of Moses Wine, back-slid ‘60s radical and bemused traveler through the ‘80s, whose last steady job provided him with a BMW that he guiltily adores. All too conscious of the recent past, he is, Angst and all, a most contemporary and entertaining detective. As it must have been remarked before, Moses Wine ages well.