AZTEC AUTUMN By Gary Jennings Forge. 380 pp. $24.95

The better a story, the less likely it will sustain a sequel. This is especially true of tragedy. There are no sequels to "Hamlet" or "King Lear." You might suppose that historical novels could be an exception to this rule. History, after all, goes on, even after kings die and kingdoms crumble. Unhappily, Gary Jennings's "Aztec Autumn" is a well-nigh Euclidean demonstration of why there is such a rule.

"Aztec," published in 1980, was a magnificent panorama of Mesoamerican civilizations as seen through the eyes of Mixtli, an Aztec Tom Jones who has a lifetime of thrilling adventures, and then the conquistadors arrive. "Aztec Autumn" reprises this material in much the same way but to diminished dramatic effect. Jennings's new hero, Tenamaxtli, Mixtli's son, is his father's carbon copy in all the wrong ways. He climbs every mountain, solves every problem, inseminates every woman in his path, and even so is doomed by the facts of Aztec history to fail at the task that occupies him throughout the book -- to lead a revolution against the Spanish occupying power. The conquest of Mexico was one of history's most awful and amazing spectacles -- a few shiploads of men on horseback taking over an entire civilization. By evoking the size and splendor of Aztec civilization in encyclopedic detail before Cortez makes his entrance, Jennings conveyed the wonder of that event as no novelist before him.

But what is left to tell -- or even to view? At the start of the sequel the palaces and temples of the Aztecs have been razed, their splendid, gruesome folkways outlawed, and the Spanish have only begun to erect their own civilization. All Jennings's considerable talent as a scene-painter and an archaeologist of the imagination are of little use.

Small wonder, with these counts against the enterprise, that the story never reaches escape velocity. Tenamaxtli goes through the motions of picaresque adventuring. He has an exemplary Aztec childhood in a northern province beyond the reach of the Spanish, has his sexual awakening and then travels to Mexico City just in time to witness his father's auto-da-fe, whereupon he vows to lead his people against the usurping Spanish. This is the task he pursues with unfailing success for the rest of the book -- until, of course, he does fail, as history requires.

Along the way, he encounters tribes inhabiting the farther reaches of his known world -- most vividly the Yaqui, a Native American equivalent of Swift's Yahoos -- cannibalistic, women-hating and real dumb. But his various encounters don't add up to a plot, as his father's did in "Aztec." He also crosses the paths of various Spaniards, but these encounters don't make a dent in his character, and he remains clueless as to the world the white men are building on the ruins of his civilization. He learns nothing except (in sometimes tiresome detail) how to make bombs and shoot muskets, and, having mastered these arts, he returns to his hometown of Aztlan and starts his recruiting effort. There he connects with an old nemesis, Yeyac, a stock homosexual villain. Lest this be read as homophobic, Yeyac is counterweighted with a good gay Aztec warrior, Nochextli. But these characters' sexuality is mere adornment, not impinging on the plot.

Similarly, Tenamaxtli's successive amours don't amount to much more than a sampling of one each from the standard menu of hard-core porn. The erotic centerpiece of the book, in which the hero spends some chapters shipwrecked on an island of women eager to be instructed in the arts of love, reads like the kind of chirpy sex manual that protests too much that sex really is fun! Enough of that and one wants to take a vow of celibacy. Without real characters, sex in novels can be as dull as the Shopping Channel.

And yet: Jennings has the essential knack of a historical novelist. He can breathe life into the dust of history and make us see from their own point of view just what the Aztecs -- and all other American natives -- were up against, the mystery the white man represented. Tenamaxtli may seem too uncannily clever at times, an Aztec Sherlock Holmes, but some real Aztecs must have done what he did and unriddled the white man's technology well enough to stage a rebellion. That much is historical fact.

As in "Aztec," Jennings is at his best in portraying a man, and a culture, that is cheerfully and zestfully bloodthirsty. The final march of the Aztec army, raping and pillaging its way from one Spanish outpost to the next (while the awful Yaqui cover themselves with martial glory in the form of Spanish scalps), is epic in size and in its logistical detail. The tale ends with the defeat of the Aztecs and a pro forma homily on multiculturalism that has all the conviction of a recitation of the rosary at the end of a pro-wrestling match.

Whatever reviews say, though, "Aztec" addicts will have to read the sequel, just as we all eat those last little bits of popcorn at the bottom of the bag, in loving memory of the first delicious kernels. The reviewer is a novelist and poet; his most recent novel is "The Priest: A Gothic Romance."