Larry McMurtry is a writer of exceptional gifts and spectacularly uneven accomplishments. His best novels -- "Leaving Cheyenne," "The Last Picture Show," "Terms of Endearment" -- are funny, moving and pungent slices of what is quite clearly real life; his collection of essays, "In a Narrow Grave," is arguably the best book ever written about Texas. But his worst novels -- "All My Friends Are Going to Be Strangers," "Somebody's Darling" -- are shapeless, purposeless, perfunctory.

"Cadillac Jack," alas, falls among McMurtry's failures -- falls with a resounding thud. Though it does have its sharp, perceptive, distinctive moments (it is impossible for me to imagine a McMurtry novel wholly devoid of such moments), overall it is a real mess of a book. To be sure, it is a brave effort on McMurtry's part, for it represents perhaps his most concerted effort to wrench himself away from Texas and locate his work in new settings; but more than anything it reveals McMurtry to be uncomfortable on alien ground and unclear about what to make of it.

The territory he has chosen is Washington, though "Cadillac Jack" is scarcely a "Washington novel" in the received sense of the term. For several years McMurtry has been a partner in a Georgetown bookstore specializing in used and rare books; this setting and this experience in merchandizing "collectible" wares seem to provide the inspiration for the new novel, the story of a footloose Texan "antiques scout" who comes to Washington to wheel and deal.

His name is Jack McGriff, but he is known as Cadillac Jack because "I do the bulk of my traveling in a pearl-colored Cadillac with peach velour interior, a comfortable vehicle in which to roam America." He is tall, roughly handsome, catnip to the ladies, several of whom he consorts with in amorous encounters that readers are likely to note more for their monotony than for their sensuality; McMurtry, whose earlier novels contain some strikingly erotic passages, here seems merely to be going through the motions.

Of these numerous women, two are of paramount importance: Cindy Sanders, "a beautiful girl social climber" who has interrupted her engagement to another fellow in order to play fast and loose with Cadillac Jack, and Jean Arber, a down-on-her-luck woman who has separated from her husband and is struggling to make a new life for herself and her two daughters. Basically it is Cindy for sex and Jean for love, though the conclusion is a trifle more complicated than that. What it boils down to is that Cadillac Jack is a man on the move, unable -- and perhaps at heart afraid -- to make lasting connections. It is a familiar theme in McMurtry's work, but he certainly has examined it in more interesting ways than he does here.

Part of the problem may be that McMurtry has surprisingly little feeling, and even less liking, for the city in which the novel is located: "Already I was getting the sense that Washington was a very cellular place. The motif of the cell recurred. All the men in trench coats and woolen hats probably spent their days in cell-like offices in vast gray buildings. Then when the government let them out they squirmed like larvae into small cell-like cars and rushed across the river or around the Beltway to vast gray apartment buildings, where they inhabited cell-like apartments." Jack McGriff's disdain for Washington is so deep and pervasive that the city as it emerges in the novel is a mere caricature, like too many of the characters in it.

Most of them have funny-ha-ha names: Cunard Cotswinkle, John C.V. Ponsonby, Schoeffer Schedel, Brisling Bowker, Bessie Lump, Cyrus Folmsbee, Sir Cripps Crisp, Khaki Descartes, Eviste Labouchere, Oblivia Brown. That a writer of McMurtry's talent and sensitivity has resorted to slapstick nomenclature in search of a few chuckles is evidence enough that "Cadillac Jack" is an entirely listless performance; if McMurtry ever had his heart in this effort, the results of it are singularly sparse -- a few amusing encounters over dinner tables in various Georgetown residences, a few touching ones with Jean Arber and her daughters, a few sly and knowing observations about the inside workings of the antiques business. But on the whole "Cadillac Jack" seems to have been assembled primarily to keep the juices flowing and to get something on paper -- a novel written, as it were, between novels.