IT WOULD BE INTERESTING to conduct a survey in order to determine which period of history has attracted the greatest number of novelists. Elizabethan England? The American Civil War? Whatever the winner, one can assert with some confidence that the Middle Paleolithic, circa 35,000 B.C., would not be among the Top Ten. Readers who have always wondered what went on back then will find not one but two books addressing themselves to the question, and a monumental question it is -- not a petty struggle between nations or ethnic groups, but the confrontation of two distinct subspecies of humanity.

Somewhere toward the end of the last Ice Age the Cro-Magnons played the Neandertals, and the Neandertals lost. The Cro-Magnons were the heroes -- modern men in all but culture -- and the Neandertals were apelike untermenschen, unworthy of survival.

That is how the scenario used to read. People who have not encountered the Cro-Magnons and the Neandertals since a fourth-grade unit on "The Cave Man" may be surprised at how scientific views of prehistoric man have changed. The beetle-browed, furry, bow-legged neandertals were smarter and less hairy than was once believed. Formerly classified as Homo neanderthalensis , a species distinct from Homo sapiens -- the intelligent ones (us) -- they have been promoted to Homo sapiens neandertalensis , a sub-species of "thinking man."

All the same, they disappeared, almost overnight in geological terms, and were replaced by populations of Homo sapiens sapiens . Anthropologists still do not know how or why. Did the Neandertals evolve into modern man? Did they die out because they were unable to adapt to ecological change their smarter cousins took in stride? Did they interbreed with Cro-Magnon man, contributing some of their genes to us? Or did the Cro-Magnons exterminate the Neandertals, in the first and most extensive genocidal war?

This greatest of all prehistoric mysteries forms the background for two novels, Dance of the Tiger and The Clan of the Cave Bear (the latter being the first of several projected volumes). Bjorn Kurten, author of the first, is a paleontologist. Jean Auel, author of The Clan of the Cave Bear , is a housewife who has done a lot of studying. She ought to fire the person who wrote her press release; the claim that she read a book in order to understand "how primitive man may have thought" is apt to inspire more amusement than respect, and it fails to do justice to her consientious research.

So few solid facts are known about this remote period that one can hardly criticize an author for filling in the canyon-sized gaps with speculation, particularly when the authorities themselves disagree. Can one, then, reasonably call these books historical (or prehistorical) novels, and demand that they conform to the rules governing that genre? I believe one can and must, if only because both authors have followed the rules to the best of their respective abilities. Known fact is not violated; conjecture is based on reasonable inferences.

The biggest problem facing a historical novelist is how to create the sense of an alien culture without losing the basic humanity of the characters. Most writers go too far in one direction or the other, producing modern men and women in funny clothes, or wax figures who gesticulate and move but never live.

One key element is the handling of language. I myself have a sneaking affection for what Josephine Tey contemptuously referred to as "writing forsoothly." An occasional "forsooth" or "by our Lady" reminds me that I am not listening to contemporaries talking. Auel and Kurten have taken the only sensible approach, since we have no Neandertal equivalent of forsooth, or of any other word. Their characters speak colloquial English. However, we are made to realize that this is only a convenient fictional device. Auel's Neandertals have a limited spoken vocabulary, amplified by a complex system of gestures. (Her heroine, a Cro-Magnon orphan adpted by a tribe of kindly Neandertals, has the dickens of a time un-learning her Homo sapiens loquacity in favor of sign language.) Kurten emphasizes the Neandertals' admiration for the more flexible, musical Cro-Magnon speech.

Both these approaches are based on what may well be the most questionable scientific theory in either book -- a recent study by Philip Liebermann which attempts to prove that the vocal apparatus of Neandertal man was incapable of producing the full range of modern sound. I would love to dissect this theory in detail, to prove how clever I am, but such analysis would be irrelevant. As Stephen Jay Gould points out in his excellent introduction to the Kurten book, Leibermann's theory is highly suspect but has not been proven wrong, and therefore it may legitimately serve as a model for a writer of fiction. The significant point is how the two authors use the model. Kurten interprets Liebermann's thesis correctly. He does not deny his neandertals a rich and complex vocabularly. They just don't talk as prettily as the Cro-Magnons. Auel's Eandertals grunt. They are a good deal more apelike, physically and mentally, than Kurtne's; and Auel's Cro-Magnon herione is a typical Aryan -- blond, blue-eyed, tall and beautiful.

This distinction is indicative of one of the major differences between these two superficially similar books. Although Auel is obviously familiar with the professional literature, she also makes considerable use of experience gleaned from survival courses and studies of homeopathic medicine. She does it well, but she is not a pro; and a professional has an adventages over an amateur, however well read. This is not academic snobbery. Kurten's professionalism shows not only in his selection of material, but in the use he makes of it. His book has an additional ease and sureness, a willingness to depart from accepted cliches, that is, in part at least, a result of long years of immersion in the subject.

Perhaps the most significant difference, however, is in literary quality. Bear is a prehistoric soap opera -- "cave opera" would be an appropriate term. Put the heroine in a bustle instead of a bearskin, and she could walk right into one of the "historical romances" crowding the bookshelves in drugstore and supermarket. Except for a few other stock characters -- the motherly wise women, the surly villain -- the rest of the cast is outstandingly undistinguished. The fact that they all have names like Oga and Aga and Uba makes it even harder to tell them apart. As cave operas go it is a good one -- slickly written, carefully researched, very sincere. But that is all it is.

Tiger is a more uneven book. In some places, particularly at the beginning, Kurten's plot squirms and wriggles and gets away from him. With the entrance of the little tribe of Neandertals the book takes off, and from then on the reader is propelled over the occasional rough spots by some remarkably fine writing and by a number of uniquely engaging characters, animal and human.

Like all good novels this one transcends commercial categories. It has elements of allegory, of fantasy, and of myth. It is also a kind of detective story, complete with a challenge to the reader. Many of the readers who solve the mystery will disagree with the solution, for it involves another highly questionable anthropological theory. But that doesn't matter. As Kurten says, "This, and the other models used, are fascinating in themselves; more importantly, they form a framework for complex and provocative questions about human beliefs and human nature. Every few pages brings a new shock of surprise or laughter, of delight or recognition. It would be unfair to Kurten, and to his potential readers, to give away any of his surprises. Read the book. It is a book for homo sapiens of both sexes, and all subspecies.