COMET. By Carl Sagan and Ann Druyan. Random House. 398 pp. $27.50; THE MYSTERY OF COMETS. By Fred L. Whipple; Assisted by Daniel W.E. Green. Smithsonian Institution Press. 276 pp. $24.95; paperback, $12.50; HALLEY'S COMET! By Francis Reddy. AstroMedia. 59 pp. Paperback, $9.95.

THESE ARE THE snows of yesteryear, the pristine remnants of the origin of the solar system, waiting frozen in the interstellar dark." And so begins Carl Sagan and Ann Druyan's tour de force. From their description of comets in general, they guide the reader through the rich history of comet lore. Sagan, an astronomer, and Druyan, his collaborator and wife, blend choice words, esoteric facts, fascinating quotes and evocative illustrations into an informative and inspiring story about one of nature's greatest treats -- Halley's comet.

Most general readers will be transfixed. And they should be, for this book outpaces the pack by provocatively answering questions such as: What would it be like to ride on a comet? Why and how have comets mesmerized humankind? Why is Halley's comet so significant? What are comets made of? How did comets affect the development of earth and the origin of life? How, with space technology, will astronomers study Halley's comet in 1986? Did comets contribute to the extinction of the dinosaurs? In the future, will earthlings be able to colonize comets?

Here we read the earliest surviving reference to a comet -- a single Chinese sentence from the 15th century B.C. We learn about the cometary myths of tribal Africans (and, given Sagan's fascination with linguistics and exotic cultures, we even learn how to pronounce a Kalahari tribe's unpronounceable name). We follow Halley through his early life to that fateful day in August 1684, when he asked his friend, Isaac Newton, about the orbits of comets and found, to his amazement, that the shy Newton had answered that baffling question years earlier but had never published the results. Step by step, we watch these men interact, each unknowingly aiding the other to become immortal.

And we learn of Halley's life -- his miserable years as deputy comptroller of the Mint and his joyous ones as science adviser and drinking partner of the young czar of Russia, later known as Peter the Great. We follow Halley in his bitter rivalry with the astronomer royal and in his sweet, long love affair with his wife. We even read the inscription his daughters engraved on their parents' tomb.

From history, Sagan and Druyan turn to astrophysics, geology and biology. In their hands, these subjects become clear, even vital. Comets, they explain, are not remote but "are a part of our planet and ourselves." Indeed, "comet stuff" covered our early planet and became part of intelligent beings here. And now this intelligence "is turning its attention to the comets from which it came."

Comet abounds with not only ideas but words. In fact, some readers may find this book too flowery, with its exuberance of adverbs ("gracefully," "ponderously," "eerily," "prettily," "stolidly"). The periodic return of Halley's comet becomes a "metronome beating out the rhythm of human progress or decline." So it goes, page after page.

FRED WHIPPLE'S The Mystery of Comets may not be so scintillating, but it is impeccably authoritative. Whipple, undoubtedly the world's foremost expert, has studied comets for half a century, largely while professor at Harvard and director of the Smithsonian Astrophysical Observatory.

In this book, he covers somewhat the same historical material as do Sagan and Druyan, albeit without the miscellanea and the flair. He excels, though, in recounting how he arrived at his own, now widely accepted, theory of the origin and composition of comets. In the late 1940s Whipple argued that the nucleus of a comet is a mass of frozen water, methane, ammonia, and carbon dioxide embedded with dust -- that is, it is a huge, dirty snowball.

In simple, direct language, he explains here what comets are and how they are studied, including descriptions of the five space probes that will fly by Halley's comet in March 1986. And he quotes a newspaper's account of a splendid experiment proposed in 1910 when it looked as if the earth would pass through the comet's tail: "Empty 24 champagne bottles and fill them with Halley's Comet cyanogen gas for future scientific tests."

For the practical, lay observer in 1986, Francis Reddy's book Halley's Comet! may be ideal. After a brief but well written and illustrated history section, it emphasizes star maps and provides advice on how best to observe the comet.

Unfortunately, despite all the fanfare many people may be disappointed in attempting to see the comet. When it is closest to the sun and thus the brightest intrinsically, it will lie nearly in the direction of the sun but beyond it. Consequently, it will be far less spectacular than in 1910 -- sad but true.

Still, Halley's will be observable with binoculars in locations with clear skies away from city lights. And the best sites will be in the Southern Hemisphere in early morning in April. There it will be visible with the naked eye.

But why do so many people care? Why do they want to see it, even if only in their mind's eye? Perhaps because they know from books they have read that Halley's is the most dramatic comet; that all comets preceded the earth; and that, as Sagan and Druyan put it, when "the rest of the solar system is dead, and the descendants of humans long ago emigrated or became extinct, the comets will still be here."