THIS IS A WESTERN. You probably don't read Westerns. Same here. Bring out a rack of Max Brands or Louis L'Amours and our eyes glaze over. But Devil at the Reins is a funny, absorbing, sure-footed Western, deftly characterized and expertly plotted.

Rope Watson -- mangy gunslinger on the outside, wry, randy and literate ex-Union Army officer on the inside -- drifts into Zodiac, Nevada, one fine spring day and drifts out the next with a contract from the town fathers on Tarquine, the czar of Primrose Flats, a bawdy, gaudy and immensely profitable red light town next door. (Primrose Flats, we are led to believe, is now known as Las Vegas.) Rope passes up several opportunities to dispatch his target quickly, turns down an offer to join the bawdy guys, and then has to run for his life when Tarquine turns loose his private police force. Holed up outside town with a tenderfoot tag-along, and hopelessly surrounded by the rabid guardians of the Flats, Walker can see as how life can be a little unfair sometimes.

Not once do events take the turn the reader expects, with Rope the loosey-goosey hero of an engaging story that ends like the crack of a rifle. It's enough to give Westerns a good name. THE FORMULA. By Steve Shagan. Morrow. 357 pp. $10.95

THERE IS A CERTAIN FORMULA to Nazi doomsday novels. It goes something like this: In the final days of World War II, when it is obvious that the Third Reich is on its way out, a small group of senior officers spirit to safety some Nazi treasure -- art, gold, children or, in the present case, the secret of producing synthetic fuel cheaply and abundantly. Many years later, the forces of right stumble onto the existence of the treasure and wage a bloody and treacherous battle to reclaim it from the forces of evil, who are about to parlay it into a climactic, world-bending coup.

Shagan is faithful to the genre. The evil force in this case is a global cartel that seems to include OPEC, big American oil, the PLO, the Mafia, cocaine merchants, a shadowy American financier in exile, the remnants of the Wehrmacht and, of course, a beautiful and tormented woman who falls in love with the hero, who is here a Los Angeles cop, late of the CIA.

All the players are thus present and accounted for, and Shagan dutifully moves them around, with plenty of sex and murder. And the premise has some basis in fact -- German efforts to produce synthetic fuel were well-known to the Allies during the war. But, that element aside, there is little original in this aptly titled novel. Shagan, who wrote the screenplay for Save the Tiger and Voyage of the Damned, treads a well-worn path. THE GLOW. By Brooks Stanwood. McGraw-Hill. 297 pp. $9.95

THE MORAL TO THE STORY: If only Jackie and Pete had maintained their poor eating habits and continued downing martinis, all would have been well. But instead this young, upwardly mobile Manhattan couple take up jogging, and run into a coven of youthful sexagenarians in Central Park. The svelte senior citizens offer Jackie and Pete an apartment in their incredibly chic (and incredibly cheap) Upper East Side building, and before long one senses that there is more to their youthfulness than yogurt and Perrier.

If, after a few chapters, you think you've guessed the plot, you probably have, and it might be wise to pass the book along to a less astute friend. Although The Glow goes down easily, there is little satisfaction in discovering, at the end, that one has been right all along. NIGHT WATCH. By Jack Olsen. Times. 308 pp. $9.95

NIGHT WATCH IS ROCK-SOLID police action. No crack units here; Jack Olsen's men -- and women -- are in the Ninth Precinct, known in the rest of the department as Lower Slobbovia, of an anonymous city. It is a precinct of flopped detectives, misfits and drunks -- some of whom are first-rate cops. When a particularly brutal murderer strikes twice in two nights, the Ninth is on the spot, and the tense manhunt brings out the best -- and worst -- of the cops as they close in on the killer.

Olsen makes you smell the rundown police station, the gray metal locker room and the garishly lit streets full of shoplifters, drifters and punks. RAINBOW. By William Harry Harding. Holt, Rinehart and Winston. 375 pp. $10.95

AN ENTERTAINING FIRST NOVEL is William Harry Harding's Rainbow. Rainbow Roberts, that is: golfer, card shark, bon vivant and, above all, con artist. His big con here is a "boat race" -- a fixed horse race -- at Saratoga in its heyday of the 1920s. But Rainbow is himself being conned by the beautiful Iris Winslow. Or so it seems. Then again, maybe not. The expert con man is really too much in love to notice.

Harding, to his credit, does more than he has to do, spinning out a pair of sharp subplots as Iris and Rainbow search for their ne'er-do-well fathers. And he has done his homework, painting Saratoga and its society, high and low, in rich colors. The frauds here are strictly honorable -- the only losers are those not quite good enough to outfox the expert, but greedy enough to try. One pleasantly suspects that the author has played a few canny Nassaus and seen a few boat races himself. THE SECOND SON. By Charles Sailor. Avon. 384 pp. Paperback, $2.75

THIS PAPERBACK ORIGINAL first novel asks what might happen if Christ had a brother who came to earth today, but did not realize that he was divine until the evidence became too persuasive to deny. Young Joseph Turner, a high-iron construction worker, leads a good-hearted but rather unremarkable life until he falls 24 stories from a building under construction. He not only survives but suffers nary a scratch. He discovers, from that point, that he can perform miracles, and the complications follow -- assasination plots, a nuclear accident, a bit of romance with a contemporary Mary Magdalen, and suggestions of the bizarre occurrences that might greet the second son of God today, including a tire company's effort to obtain his endorsement.

Sailor tries to accomplish a bit too much, anxious to explore anything and everything that might occur should an emissary of heaven come among us. But Second Son is ingriguing and enjoyable reading, and Joseph Turner a credible, if reluctant, messiah.