BIG FISH. By Thomas Perry. Scribners. 248 pp. $15.95; HEAT. By William Goldman. Warner. 244. $15.50.

ALTMEYER AND his wife Rachel live in the hills outside Los Angeles. They keep goats and have a pond full of koi, and they support all of this by selling military weaponry to American survivalists, Afghan rebels, and a trio of Japanese named Mr. Bridges, Mr. Walker and Mr. Bone. Their neighbor, Bucky Carmichael, enlists their help; he is a high-powered Hollywood agent who has been doublecrossed in a cocaine transaction, and now the man who cheated him is going to make things worse by killing him.

The Altmeyers, whose incessant repartee suggests they watched too many Nick and Nora Charles movies at an impressionable age, quip their way to Bucky's salvation. (After all, he once lent them his food processor.) Success crowns their efforts, and Bucky is readily persuaded to invest the proceeds of this venture in Altmeyer's Japanese enterprise. The three scoot down to Ensenada to watch as a load of guns is packed into bales of cotton, and are nearly blown up for their troubles. So off they go to Japan to set things right.

There they learn the gun deal was only the cover for a larger operation, with the threat of (gulp!) global nuclear blackmail. They bounce around the world, to Brussels and L.A. and London, enlisting en route one Arthur Paston, a client of Bucky's who has been directing films and mixing perfect martinis for something like 60 years.

Thomas Perry, who has put all of this together, is a writer of much imagination and considerable skill. He handles action nicely, schemes cleverly and allows his characters to kill without a second thought whenever they find it expedient to do so. All the same one warms to his people, even when they are being too cute, which is most of the time.

Perry's first novel, The Butcher's Boy, was wonderfully taut and suspenseful. His second, Metzger's Dog, maintained suspense while being utterly hilarious in the bargain. Big Fish does not work as well as either of its predecessors, and one wonders why.

There is, for openers, a curious lack of tension. One senses early on that the Altmeyers and their friends are charmed, that nothing can possibly touch them, and that they themselves have peeked at the book's final pages and know they have nothing to worry about. Only the bad guys get killed, and they remain faceless throughout. The novel's violence is oddly bloodless, as if even the victims are unaffected by it. The humor, too, is never much more than clever; Metzger's Dog was rollickingly funny, and this book isn't.

LACK OF TENSION has never been a problem for William Goldman, who has shown himself capable over the past three decades of writing virtually every kind of book but a dull one. Heat is the story of Nick Escalante, a sort of civilian of fortune, master of edged weapons and the most dangerous man alive inside of 20 feet. He lives in Las Vegas and loathes it, sustaining himself with dreams of travel. He needs $100,000 for the five years of uninterrupted travel he has promised himself, and the book opens on his 5,000th day in Vegas with his finances only $99,700 short of his goal.

In the book's brief span, Nick must bodyguard a nervous Bostonian low roller, help a reformed TV evangelist cope with a mad extortionist, avenge a friendly hooker's savage mistreatment at the hands of a visiting Mafioso, keep from getting killed by the most dangerous man in the world outside of 20 feet, and turn his $300 into the bankroll he needs to make his dreams come true. There are, as one might gather, not a lot of uneventfulpages in this book.

More than anything else, Goldman is a magician, an illusionist, a master of prose legerdemain. No one in his novels can be safely trusted, the author least of all. In Control one is more than halfway through the book before realizing it has been artfully set a century earlier than one has assumed. In The Color of Light, the reader finished a scene before coming to understand that more than a year had slipped by between it and the preceding scene. In other works, action sequences which seem actually to have taken place turn out to have occurred only in a character's fantasies. One can take nothing for granted.

There is a fair amount of this trickery in Heat, and I would not dream of spoiling Goldman's fun. He does this sort of thing superbly, but it is by no means all that he does well here. All of the book's subordinate characters, the dealers and pit bosses and hoodlums and compulsive gamblers of the Vegas demimonde, come vividly to life. Goldman has always been particularly good at portraying compulsive behavior -- one thinks of the ingenious anorexic in Tinsel -- and his rendition of a gambling binge is almost too painfully real to read.

The book is, ultimately, very much about violence, its title a reference to the physical sensation Nick feels before going into action. We are told that Nick was interviewed for a book called Our Friend Violence, and violence is indeed a friend in this novel, its appearance disquietingly comforting. There is one astonishing sequence in which Nick disposes of three armed adversaries in 18 seconds, each of those seconds meticulously described in an individual paragraph. I suppose this is the prose equivalent of the slo-mo action scenes in films; it is wonderfully effective in print.

Far fewer corpses pile up in Heat than in Big Fish, but Goldman's violence is at once more genuine, more emotionally satisfying, and finally more disturbing. There are some plot elements which strain credibility, along with an ending some may find unsatisfying, and I personally could have done without the hired assassin who tells old jokes at great length, but that's minor. Both of these novels are the sort you're likely to read at a single sitting; each is the work of an author who seems quite incapable of writing an awkward sentence.