Stix Dix Fix Nix : KILLSHOT <i> by Elmore Leonard (Arbor House: $18.95; 288 pp.)</i>

Neither middle-aged Armand Degas (a.k.a. The Chief, or “The Blackbird”) nor his younger side-kick, Richie Nix--he with his “It’s Nice to Be Nice” T-shirt--are the sort who spell anything but trouble if encountered in a darkened alleyway. A squat, Ojibway Indian living in Toronto, Degas is a contract killer for the Mob, free-lancing in the Detroit-Ontario area. And, at least, there’s a reason behind his killings. He’s being paid.

Mercurial, borderline-psychopath Nix, whose only real ambition is to knock off a bank in every state (“except Alaska, forget it”), and who still has 37 states to go, is less predictable. Call it whim or hunch, killing is a more casual affair with Nix and darned if he can remember exactly how many souls he has dispatched because he keeps losing count--depending on what age he chooses as his starting point.

A strange partnership, indeed, that begins when Nix tries to steal Armand’s new Cadillac, which would normally be a fatal miscalculation and blossoms, inexplicably, when the otherwise level-headed Ojibway lets his bubble-headed companion talk him into an extortion plan against a Detroit- area real estate developer. A plan that has all the deftness and subtlety of an attack with a claw hammer.

Suddenly swept up in this amateur-hour larceny, and another one of Nix’s off-the-cuff homicides, are the decent, blue-collar Colsons, Carmen and Wayne. A high-rise, structural iron worker perfectly at home strolling along a 10-inch beam 30 stories above the ground, Wayne is hardly cowed by this homicidal Mutt-and-Jeff team, but Carmen--working as a part-timer for the developer as a part of her self-improvement program--is another matter. As the only witnesses who can nail Degas and Nix to both the extortion plot and the murder, the gun-happy pair will settle for either, but preferably both, of the Colson heads.

Against their better instincts, Wayne and Carmen allow themselves to be swept into the Federal Witness Protection Program and relocated to a fly-trap abandoned house in Cape Girardeau, Mo., on the banks of the Mississippi--just the spot for a displaced iron worker, trained to build skyscrapers, to find gainful employment. And, in short order, the inept and libidinous deputy U.S. marshal assigned to protect them is enough to make Carmen, at least, almost wistful for the old days when the only menace hanging over her was a couple of lethal gunmen.

Author Elmore Leonard, with the taste of such successes as “Stick,” “Glitz” and “Freaky Deaky” still fresh in his mouth, has a masterful touch with characterization and, in the Colsons, he’s created a wry, likable couple who have a touchingly tender affection for each other and, in their own way, are every bit as tough . . . 10 times brighter . . . than the lethal Yo-Yos stalking them. And the villains, the stolid, menacing Armand Degas and his loose-cannon companion, Richie Nix, are sinister in every dark meaning of the word--Degas, because he is so unwaveringly predictable in his murderous intentions, and Nix because he is so bone-chilling in his un predictability.

And the path is strewn with minor, gemlike characters like Ferris Britton, the sleek, body-building, deputy marshal who is never quite sure of what he is supposed to be doing in protecting the Colsons but, we suspect, would do it badly even if he did know. And then there’s 50-ish Donna Mulry, cashiered out after 25 years as a food service officer in a correctional institution who remains a jail bird groupie, and who shelters the two killers.

Poor Donna and her endless supply of TV-dinners for Armand and Richie because she’s never learned to prepare food for fewer than 1,200 felons at a time. And then there’s the question of Carmen’s mother, Leonore, who retired from Michigan Bell, but remains one of the utility’s best customers. Can Leonore, who can talk endlessly into a dead phone simply because it’s there , be trusted to keep the Colsons’ relocation a secret?

“Killshot” is a riveting page-turner, a hare-and-hounds chase through the bleak suburbs of Detroit and the seamy riverfront dives of Cape Girardeau. Leonard’s dialogue, as is usual with him, crackles like the riveting torch that Wayne Colson handles so deftly 100 feet above the hard ground.

Richie Nix bought a T-shirt at Henry’s restaurant in Algonac that had IT’S NICE TO BE NICE written across the front. He changed in the men’s room: took off his old T-shirt and threw it away, put on the new one looking at himself in the mirror, but then didn’t know what to do with his gun. . . . What he did was roll the .38 up inside the jacket and carried it into the dining area.

There was a big IT’S NICE TO BE NICE wood-carved sign on the shellacked knotty-pine wall in the main room, over past the salad bar. It had been the restaurant’s slogan for fifty years. . . . Richie Nix took a table off to the side where he could look at freighters and ore carriers if he wanted, though he was more interested this evening in keeping an eye on the restaurant parking lot. He needed a car for a new business he was getting into. . . .

He watched an ’86 Cadillac pull into the lot and park. Baby blue with an Ontario plate. Richie liked it right away. He watched the guy get out of the car, short and stocky, his hair slicked back, adjusting his coat, Jesus, getting ready to make his entrance. . . . It’s nice to be nice, Richie thought, staring at the guy and working himself up to what he was going to do. But I got news for you. . . .

From “Killshot”