DESPITE THE ENTREATIES of Lee Iacocca and others, about the only good reason for "buying Detroit" in today's economy is Elmore Leonard. Though not Motor City's only thriller writer, Leonard's the best, and, to use the local idiom, he beats the competition for smooth handling and tough performance. Of course, one major difference between an automobile and a finely tuned Elmore Leonard crime novel is this: a car has no plot. Leonard, on the other hand, gets so much mileage out of his that just when you think one is cruising to a stop, it picks up speed for a few more twists and turns.

However, though he's written 14 earlier novels (several of them westerns), each better than the last, Leonard has, until recently, been little known. Now, with Cat Chaser's publication following not too long after the flurry of praise that accompanied Split Images, the '81 model Leonard, that situation should be remedied. I, for one, am volunteering for charter membership in the Addicts of Elmore Leonard. Rarely have I felt in such capable authorial hands, rarely have I experienced such a blending of violence and benevolence. It's like stepping into a slightly dancing ocean at perfect temperature: the potential for great harm is there but somehow, against the odds, everything's under control and it feels great.

Split Images was set in Detroit, where most of Leonard's other stories have taken place, and also in southern Florida. Cat Chaser is an all-Florida book and, while it's a Florida John D. MacDonald would recognize, it's a moral landscape Graham Greene would feel at home in. Evil exists in Leonard's novels--a casually dressed Evil, wearing a wrinkled seersucker jacket (Cat Chaser) or a K-Mart cowboy hat (City Primeval). And the idea of Good has evolved throughout the Leonard oeuvre until it stands perfectly personified in Cat Chaser by George Moran, proprietor of the Coconut Palms Motel. No matter that he makes love to another man's wife or commits murder, Moran's as good a guy as they come, and he possesses an almost cosmic cool. At times, even, his self- possession seems that of an innocent, someone who doesn't know that when a gun goes bang it's often lethal, who doesn't know that cuckolded husbands can be homicidally inclined.

Yet, Moran, a Marine veteran of the 1965 invasion of the Dominican Republic, lost his innocence long ago; what he's held on to is his decency. This quality Leonard conveys just beautifully, along with his hero's insouciant iconoclasm. Yet, as free spirits go, Moran's not too extreme. He's the sort of fellow who thinks that it isn't really necessary to knock yourself out to earn more money than you can spend and that just because you live in Florida you don't have to wear white shoes. His ex-wife had other complaints: "not wearing the outfits she bought him with little animals and polo players on them . . . not staying on his side of the court when they played mixed doubles and she never moved . . . drinking beer out of the can . . . not having his Marine Corps tattoo removed . . . growing a beard. A lot of little picky things like that."

And here's what Mary de Boya, his lover, discovers: "there was much more to Moran than a natural, easygoing manner. At times he seemed almost naive, yet he continued to surprise her."

Mary, who's married to a millionaire Dominican exile (under Trujillo, Andres de Boya was a general specializing in methods of torture), is from the same hometown as Moran. Detroit, naturally. The two of them, Moran and Mary, were powerfully attracted to each other at their first meeting, but the moment wasn't right. Now, as Cat Chaser gets under way, they meet again, in the Dominican Republic. Mary's gone there with some bored women friends to watch the polo; Moran's on a sentimental journey to try and find the young girl (now practically a middle-aged woman) who, 16 years before, had been the enemy on the streets of Santo Domingo. Wounding George, capturing him, she'd also captivated him--though not romantically, or at least not in the erotic sense of the word--and to lay to rest the ghost of that senseless invasion, he wants to see her again. The name of Moran's platoon was "Cat Chaser."

A surprise encounter in a foreign counry can go a long way towards letting down the flood gates of suppressed passion; this being the case, Moran and Mary quickly fall into each other's arms and swear never to part. The only obstacle to their devotion is Mary's admission that she likes being rich: she's willing to divorce de Boya, but what about the two million he promised her in a pre- nuptial agreement? Though this scenario may sound like a familiar one, trust Elmore Leonard, who apparently has no taste for James M. Cain-type doomed losers.

For most writers, such a situation would be enough to propel a novel from beginning to end. But this is a vehicle manufactured by Elmore Leonard, and so the affair between Moran and Mary, as well as Moran's search for a part of his past, are only component parts of the plot machinery. As in all of Leonard's books that I've read, there are in Cat Chaser some wonderfully meaty roles for character actors; here, each of them--the jovial but sinister Irishman, Jiggs Scully, the ex-dinner theater actor-turned-investigator, Nolen Tyner (who'd rather drink beer around Moran's motel pool than do stake- outs), the hustler, Rafi Amado, who's got more greed than brains--helps to account for the dizzying pleasure of the plot's intricate route. By the time the book closes (a finish that bears some similarity to that of City Primeval), after a mere 283 pages, the angles that informed its first chapters have been lost in the dust.

The hard-boiled paladin, from Philip Marlowe to Travis McGee, is the tradition from which George Moran springs. Not a series character (other Leonard titles feature petty crooks or cops in the lead roles), he's appealing enough to make a reader want more. But the satisfactions of Cat Chaser and the rest of Leonard are more than the charm of his heroes and the richness of his supporting cast, more even than his twisty plots. It's become a clich,e, to acclaim creative works as "American," but that, I think, is what the sum of the Leonard parts is--sunshine and violence, optimism and disarray, filtered through Leonard's own forthright individualism and consistently lightened by his quizzical humor.