TWO NOVEL APPROACHES TO MAN'S ORIGINS.

Byline: Helene Lorber Knight-Ridder Tribune News Wire

Title: ``Neanderthal''

Author: John Darnston

Data: 368 pages, Random House; $24

Our rating: Three Stars

Title: ``Almost Adam''

Author: Petru Popescu

Data: 544 pages, William Morrow; $24

Our rating: Three Stars

Two novels, alike, but with distinct differences. Two authors, on book tours, traveling thousands of miles, meeting hostile native inhabitants. Two movie deals, their dollars measured in geological terms. Will they destroy each other in a mighty clash, leaving scant evidence for future investigators in remainder bins, or coexist, forming mighty branches on the best-seller lists?

Forgive the hyperbole, but I get apocalyptic where the antecedents of the human race are concerned. In other words, I love a good caveman book, fiction or nonfiction.

Now two novels take a new approach - modern humans come into contact with members of the Homo genus further down our family tree.

In ``Neanderthal,'' the conceit is pretty clever: There is evidence that Homo sapiens sapiens and Homo sapiens neanderthalensis coexisted in Europe during the last ice age, about 25,000 years ago. In many ways, the Neanderthals were better adapted to the extreme conditions of the time than we were. Why and how they became extinct has been the subject of fascinating scientific conjecture. John Darnton postulates that they did not die out. In battle after battle with modern humans, his novel says, they were driven further and further into hostile territory that they could tolerate and we could not. They have lived for 25 millennia high in the remote Pamir Mountains in Tajikistan, surfacing occasionally, and then known as Yeti, Sasquatch or Bigfoot.

But now time has caught up with them. Word of their presence is leaking out into the scientific world. In fact, Dr. Jerome Kellicut, the famous Harvard paleontologist who mounted an expedition to find them, is missing. A shady, CIA-backed think tank enlists two of his former students, Matt Mattison and Susan Arnot, lovers long ago, now academic rivals, to find him.

It's not giving away anything to reveal that they do. He's living among Neanderthal hippies who have found the best piece of real estate in the Pamirs, a cozy spot with a subtropical microclimate. They're peaceful, they're vegetarians, they communicate telepathically - they'd be completely blissed out if it weren't for the other Neanderthals, the nasty warlike ones, living in the cave on the other side of the burial ground.

Matt and Susan have a variety of dilemmas: Do they shout to the world about the astounding discovery, risking the future of the species? Do they continue to assist the spooks who want to capture the power of telepathy? Do they help one group over another, thereby violating the basic scientific tenet of observing without influencing?

While they're struggling with this, the reader is struggling with more red herrings than there are in Minsk. Were they necessary? No. Isn't it enough to have a colony of Neanderthals alive and well in 1996? Darnton mucks up the story with too many useless details instead of concentrating on what's important. Like his characters. Matt has got to be one of the least appealing heroes ever.

Still, the nonstop action and diversions, which detract from the book, ought to make ``Neanderthal'' a swell movie, especially in the hands of Steven Spielberg's Dreamworks SKG, which has purchased it.

``Almost Adam'' ought to make a good movie, too, but more to the point, it makes a good book right now. Never mind this 25,000 years stuff - it pops back 2 million years to find its lead character.

It all starts when paleontologists Ken Lauder, an American, and his Kenyan friend and colleague, Ngili Ngiamena, fly over what they believe are fossilized footprints on a rock outcropping in a remote area of Kenya. When they land near the site, they make an even more startling discovery - a nearly complete skeleton of an australopithecine, a human ancestor of 2 million years ago.

Buoyed by the discovery, the two plan to return with proper equipment and supplies to launch a full-scale camp. But Ngili's father, a member of Kenya's ruling elite, has other plans for his son, and Ken must return alone.

The loss of Ngili's company and expertise turns out to be the least of Ken's problems. No sooner does he arrive at the site than he's beset by men who try to kill him for no reason he can fathom. He escapes into the bush, and into a remarkable adventure.

It seems that the geology of the area has prevented the kind of climatic change that forced hominids from the forest onto the savanna, and into upright walking and other evolutionary developments. Before too long, Ken, weakened by hunger and thirst, comes upon a specimen of humanity as unchanged as the climate - an 8-year-old prehistoric boy. The two forge a strong bond that serves them well as forces of both their societies intrude on their peace.

The prehistoric beings in ``Almost Adam'' have more personality than the humans of ``Neanderthal.'' The boy, Long Toes, hides his loneliness with bravado. The alpha female of his clan is wise and firm. The human characters are also well-drawn - the drunken pilot, mourning the bad old days of colonialism; the corrupt police chief, happy to sell out his country for personal gain; the great white paleontologist, avidly eager for recognition.

We Homo sapiens are stuck with words for communication (even ``Almost Adam's'' hominids use telepathy), but Popescu has used those words to compelling effect.

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Photo: no caption (Book cover - NEANDERTHAL)