THE MAN WHO RODE MIDNIGHT By Elmer Kelton Doubleday. 261 pp. $16.95

If this were the best of all possible worlds, and if fate traveled in straight lines rather than ellipses, Elmer Kelton would be a household name right alongside Louis L'Amour.

Kelton, like L'Amour, has spent the better part of a lifetime (more than 25 novels in the last 33 years) working within, and occasionally transcending, the genre of the western novel.

After years of working in the pulps (his earliest novels were written under pseudonyms such as Alex Hawks), Kelton first started gaining serious critical recognition about a decade and a half ago. That's when he began turning his impressive descriptive powers and rather vast knowledge of frontier history to more ambitious and fully realized works like "The Time It Never Rained" and "The Wolf and the Buffalo."

These books, with their skillfully woven narratives and elaborate backdrops of history and colliding cultures, were actually masterfully wrought historical novels in the more readily identifiable (and marketable) guise of westerns.

In fact, ever since I read "The Wolf and the Buffalo," Kelton's 1980 epic about the travails of the first black men to serve as frontier cavalrymen, I have been left with the inescapable feeling that if fate did not follow such elliptical lines, then the Texan Kelton, instead of a well-meaning if only slightly less inspired interloper like James Michener, would have written the blockbuster "Texas"; it would have been a much meatier book if he had.

Perhaps it is all these lofty expectations that make "The Man Who Rode Midnight," Kelton's latest novel, seem a bit of a disappointment, as well as a step down from the epic heights he has been scaling more recently.

Although the landscape in his new novel is still his beloved west Texas (where practically all of his books take place), the setting is contemporary. The villains this time are not corrupt cattle barons or murderous bands of renegade Comanches, but greedy land developers with dollar signs in their eyes. It is their ambition to flood the family-held ranch lands around the diminutive cattle town of Big River and build an artificial lake and resort where city folks from Dallas can come to water-ski and play miniature golf.

Standing in the way of this vision of progress is one stubborn, wizened and solitary old cattle rancher named Wes Hendrix. Hendrix, it seems, is fiercely attached to the barren and heavily mortgaged piece of scrub land from which he's eked out a living for most of his life, and which happens also to be right in the middle of the proposed lake.

As the story progresses, it is a tribute to Kelton's skill and subtlety that it becomes somewhat difficult to pick out the characters wearing white hats from those wearing black ones. Despite the rather noble and courageous sentiments behind Hendrix's resistance to change, it soon becomes apparent that the ranchers-versus-developers crisis is actually a bit more complex than it appears. True, the lake project, and the flocks of tourists who will surely follow, will mean the end to Wes' ranch and others like it. Without the lake, on the other hand, there will be no economic salvation for Big River and the surrounding rural economy, which is in the process of drying up and blowing away.

Perhaps it is only because it comes in the shadow of a masterpiece like "The Wolf and the Buffalo" (which was reissued last year by Texas Christian University Press) that "The Man Who Rode Midnight" -- particularly the latter half of the book -- seems to fall a bit flat.

Admittedly, the characters are movingly drawn, as are Kelton's descriptions of the bleakly beautiful landscape of live oaks and limestone arroyos. Unfortunately, too much of the dialogue, not to mention the blithely serendipitous ending, could have been lifted straight from an old Roy Rogers movie.

Then again, maybe "The Man Who Rode Midnight" is the kind of book that Kelton has to turn back to now and again to stay tuned to that vast readership out there. If so, then maybe it will give him the financial freedom to turn out a few more books like "The Wolf and the Buffalo," in which his formidable talents are so much more fully represented. The reviewer is at work on a book about John Wilkes Booth and the Booth family of Maryland