LONESOME DOVE. By Larry McMurtry. Simon and Schuster. 843 pp. $18.95.

LONESOME DOVE is a very small Texas town, right on the Mexican border. In it, somewhere around the year 1880, live two former captains in the Texas Rangers: Woodrow Call and Augustus McCrae. Both are in vigorous middle age.

These days they are running a combination ranch and livery stable -- or at least Call is. Gus McCrae mainly loafs around the ranchhouse with a whiskey jug, though he does participate in night raids into Mexico to steal horses and cattle. (Sometimes they are merely reclaiming stock which Pedro Flores, the fierce hacienda owner to the south, had previously crossed the river to steal in Texas. Traffic both ways is brisk.)

Call, though a compulsive worker, doesn't do everything on the ranch himself. There's also a small crew: Pea Eye, a former corporal in the Rangers; Bolivar, a former Mexican bandit turned cook; Deets, a black cowboy and the best tracker in Texas; and Newt, a 17- year-old boy. There's other company in Lonesome Dove as well: an exceptionally beautiful (and morose) whore named Lorena, a piano player named Lippy with a hole in his stomach, an independent young widow named Mary Cole, and so on.

This could be the beginning of any number of western novels. All the standard elements are present. Turn the key, and the clockwork figures will start shooting, drinking, roping cows, whoring . . .

It happens instead to be the start of one of the best westerns I have ever read. It certainly is the best of Larry McMurtry's, and he has written good ones before.

One thing that makes the book so good is the sheer sweep of the plot. Quite early on -- though not before we've been on a night raid to Mexico and encountered herds moving both ways -- the two Ranger captains decide to pull up stakes and go to Montana. Texas has gotten too tame for them. Call's idea is to be the first rancher in Montana Territory.

Since they take about 3,000 cattle with them, they need more hands than just Pea Eye, Deets, and the boy Newt. They hire half a dozen cowboys, including a top hand named Dish Boggett, one of the most appealing characters in this or any western. In the end, quite a lot of other people go, too. They include still another former Ranger named Jake Spoon, two young Irishmen whom the captains found in Mexico (the immigrant ship took them to Vera Cruz) and Lorena. Lorena goes because she has fallen in love with Jake. Jake takes baths.

Most of the book is taken up with innumerable adventures that occur on this long journey. McMurtry never falters. Each river crossing or Indian fight or meeting with settlers or encounter with the U.S. Cavalry (a sorry lot, in this book) is freshly realized. There is the same sense of grand drama that you get from going down the river with Huck and Jim -- and the same generous helping of tragedy within a humorous book, too.

EXCEPT in this way, though, Lonesome Dove is not much like Huckleberry Finn. It is, quite amazingly for a western, more like the novels of that mannered Englishwoman, Ivy Compton-Burnett.

What I mean by that is that the book has a great many scenes in which nothing happens except that people talk -- and they talk so well you never want them to stop. This is a rare thing in westerns. It is rare even in the novels of Larry McMurtry. He has, of course, been a gifted writer of dialogue right along -- way back since Horseman, Pass By in 1961.

But his subject matter (when it hasn't been Hollywood) has been Texas, and the convention in Texas movels and westerns in general has been that good people aren't articulate -- or bad ones, either, usually. Strength and silence go together. Some little prissy weak-willed easterner may gab a lot, but westerners speak through action. True, one special variety of straight-faced joking has always been allowed, even encouraged, but that's a limited vein to mine.

McMurtry's success with Lonesome Dove comes in great part from the wonderful talkers with which the book is filled. Three of them stand out: Gus McCrae; a tough rancher named Wilbarger who claims to have gone to Yale when young; and a brilliant woman around 40 named Clara, whom Gus once hoped to make his third wife. The book is 800 pages long; I would gladly have listened to any of the three for another 800 pages. I couldn't of course, because by the end Gus and Wilbarger are both dead. But I still hope to hear Clara's voice again someday. Not to mention that of Po Campo, the remarkable cook who replaces Bolivar when he quits and returns to Mexico.

How can a book stay a western with all this talk? Easy. For every conversationalist, there are two or three silent people. Captain Call hates chatter as much as Gus loves it. Lorena almost never speaks to a customer. There is a buffalo hunter named Big Zwey who can easily go a week between sentences. The combination works.

The book is not, of course, perfect. It has at least three faults, one of which it shares with the work of Compton-Burnett. Her dialogue may be three-dimensional, but her characters are mostly one-dimensional. So are most of McMurtry's. In fact, many of them don't have even one dimension, they just have a single trait. Big Zwey's is his helpless silent unrequited love for an ex-whore named Elmira. Bolivar's is his passion for beating dinner bells with a broken crowbar. One cowboy is recognizable chiefly by his habit of vomiting whenever he gets drunk, which he does at every possible opportunity.

McMurtry has been devising one-trait characters all his life. Billy, back in The Last Picture Show, cared only about sweeping with a broom, and often swept his way right out the poolroom door in Thalia, Texas, and on to the outskirts of town. There are such people in almost every McMurtry book; they are a useful device when you're writing broad humor. But Lonesome Dove is deeper and sadder and more complex than these early books, and in its context the one-trait characters sometimes become an irritant.

A second flaw in the book is that it changes tone about a hundred pages in. I suspect that McMurtry originally intended a more superficial and more easily humorous book than the one he wound up writing.

And a third flaw is that he keeps introducing characters that he then makes no use of. The two Irish immigrants, for example. The blue pigs (special pets of Gus) that accompany the drive all the way to Montana. Mary Cole.

It would be an ungrateful critic indeed, though, who spent much time worrying about flaws -- or even who wondered too much why it is that with only one exception the women in the book are bored and disgusted by men who love them. The only sensible response to this book is to do a little dance of pleasure, and then to start hoping that McMurtry has another one as good still in him. 90:By Noel Perrin; Noel Perrin is the author of "First Person Rural: Essays of a Sometime Farmer" and its successors, "Second Person Rural" and "Third Person Rural."