Take the DNA Train : THE GOLD BUG VARIATIONS, <i> By Richard Powers (William Morrow: $25; 639 pp.)</i>

Let’s begin with the “Youngblood Hawke” theory of fiction, promulgated by the hero of a forgotten Herman Wouk novel. To engage us seriously, says Hawke, a rumpled, expansive young writer modeled on Thomas Wolfe, a story must offer the equivalent of a “lovely, helpless girl tied to the railroad tracks . . . the wind blowing her skirts up around those pretty legs . . . and that train thundering around the mountain pass.”

Hawke goes on: “Dostoyevsky tied that girl on the tracks in the first 50 pages of every book he ever wrote. Henry James . . . never wrote about anything else, hardly. Dickens had . . . avalanches coming down from both sides. Joyce didn’t, no. That’s why only English teachers read him.”

Granted that Joyce has lasted and Wolfe has not, where does this leave Richard Powers’ brilliant, ambitious third novel? Will only English teachers, molecular biologists, computer programmers, musicologists and art historians respond to it? Or is there something in these dizzying 639 pages of wit and erudition to make the rest of us care, too?

There is. Powers, in effect, ties all humanity to the tracks; his train carries the heaviest metaphysical freight. It’s the same train whose far-off whistle alarmed fundamentalist Christians a century ago, rumbling down the rails laid by Darwin’s “On the Origin of Species.” Now it’s highballing toward us, stoked by James Watson’s and Francis Crick’s discovery of the double-helix structure of the DNA molecule in 1953.

That scientific feat, Powers asserts, ushered in a supreme moment that most of us have simply failed to recognize. For 3 billion years, in a random, unrepeatable and infinitely complex process, the four nucleotide bases, or chemical building blocks, that make up all life on Earth have reproduced themselves and mutated into bacteria, dinosaurs and, finally, a species that right now is cracking the genetic code that has shaped all that behavior from the beginning, including this circular act of self-discovery.

Stuart Ressler recognizes the moment and tries to seize it. A gifted, ascetic young researcher, he arrives at the University of Illinois in 1957 to join a team taking one of the first whacks at the code. He is inspired by Poe’s story “The Gold Bug,” which is about code-breaking, and by Bach’s “Goldberg Variations,” a recording of which he is given by Jeanette Koss, a married colleague. Ressler comes very close to success--close enough to get his picture in Life magazine.

Then what? In 1983, we find him in a dead-end, graveyard-shift job at a computer database firm in Brooklyn. A fellow worker, Franklin Todd, senses Ressler’s buried immensity and enlists librarian Jan O’Deigh in cracking the code that this celibate recluse has become. (Their search for the reasons why Ressler dropped out recalls Powers’ first novel, “Three Farmers on Their Way to a Dance,” in which a 1914 photograph of young men about to be swallowed up by World War I is the subject of an inquiry into how our whole century lost its innocence.)

Todd and O’Deigh fall in love, like Ressler and Koss 25 years before them. The troubled histories of these two relationships intertwine like the complementary helixes of DNA.

Moreover, the novel is structured exactly like the “Goldbergs,” Ressler’s favorite metaphor for the life process: a chapter for each of the 32 variations--arias, dances, arabesques, canons; a repetitive pattern that spawns dazzling variety.

Ressler has another metaphor: Jacob’s ladder, the biblical dream stairway between Earth and Heaven. But his research doesn’t point to anything divine in the biblical sense. We are the product of processes that don’t care about us as individuals, as would-be immortal souls. Even our species is merely something the four bases have cooked up for their own convenience. The human experiment need not succeed; in fact, we may be discovering our genetic heritage only in time to learn that we have tampered with it, and fouled our environment, beyond recovery.

Like the rest of late-20th-Century civilization, Powers’ characters, with their near-genius IQs and access to libraries and computers, are swamped with information. They yearn for values, which alone can transform information into knowledge. But where can values come from today? “The world’s pattern was not assembled for the mind’s comprehension,” O’Deigh reflects, peering into the same abyss as Ressler. “Rather the other way around. . . . That made (it) more miraculous.” But it’s not the miracle we sought.

We are familiar with the reductionist effect of science, its “only X” quality. Love is only chemicals. The moon is only a place where an astronaut hit golf shots. The thing about Ressler--the reason Todd and O’Deigh are so profoundly drawn to him--is that he tries to transcend this way of thinking, and sometimes succeeds. Meeting a neighbor’s 9-year-old daughter, he sees her as the sum of her amino acids and enzymes, but he doesn’t reduce her to them; instead, he embraces the unwanted miracle and bursts into tears, awed by the magnificence of their functioning in her.

Still, Ressler is traumatized by his discoveries. He tries to find value in love, though he has learned that our very impulses to love and to create values have been encoded in our genes by an accident of doubtful evolutionary utility. Koss, however, cannot bear children. She returns to her husband, after which Ressler lives alone and turns from science to music. Sterility haunts the younger couple, too. Todd delays giving birth to his doctoral thesis; O’Deigh, full of information about genetic defects, has had her tubes tied.

“The Gold Bug Variations,” ultimately, is about how these four people become fertile after all, like the four base chemicals, like the notes of Bach’s base tune. Like this novel itself.

For Powers doesn’t just create a beautiful form, an ingenious intellectual construct. He makes his characters live. Not a scene--faculty party, romantic tryst, walk in the zoo, computer scam--is written routinely. Curiosity shines on every page, as it does in Ressler’s ideal of science, whose aim isn’t “stockpiling brutal efficiency, accomplishing the sadistic myth of progress,” but cultivating “a perpetual state of wonder.”

True, Powers, like Joyce, has limited his audience by disdaining the usual sources of fictional excitement. To describe the modern crisis of the spirit, he has relied on frontal assault, and frontal assaults, in literature as in war, are costly. Characters capable of analyzing such a crisis are, of necessity, a rarefied, untypical bunch. A lot of readers are going to skip or skim long stretches of science writing, music theory and art appreciation. But others--those for whom the approaching train isn’t a phantom, who can feel the vibration of the rails in their guts--will find this book essential.