Man of Two Worlds by Frank Herbert and Brian Herbert (Putnam’s: $18.95; 464 pp.)

Frank Herbert died earlier this year at age 65, leaving the world of science fiction a wonderful legacy of powerful novels.

He also left the publishing industry a rich gift: the knowledge that science-fiction novels can find a wide audience. It was Herbert’s “Dune” series, more than any other writer’s work, that brought science fiction to the best-seller lists regularly.

Finished shortly before his death, “Man of Two Worlds” has all the elements of Herbert’s epochal “Dune” novels: grand visions of the universe, a battle between two civilizations, a “spice” that is a powerful drug, machinations within schemes within plots, godlike figures who tinker with human destinies, beautiful women, deadly assassins--even a giant worm, albeit a mechanical one.

Frank Herbert’s last novel was written with his son, Brian, author of five previous books. “Man of Two Worlds” has an undertone of humor that is totally lacking in Herbert’s other works. Brian can be thanked for that. Although his father was as jolly a man as ever lived, Frank’s novels were utterly serious. Brian is the one who writes humor.

The novel deals literally with the basic agony and ecstasy of storytelling. An alien race, called Dreens, created the Earth and the human race as a story told on Dreenor, their home world.

All Dreens must tell stories because on Dreenor, stories are the coin of the realm. The high priestess/queen of Dreenor is the Supreme Tax Collector, and her subjects pay their taxes with stories--stories that create reality. What a wonderful conceit!

But Herbert pere et fils are not content with merely displaying a clever idea. They show that the humans in the Dreens’ story of Earth take over their own destiny and begin to shape the destiny of Dreenor itself. The creatures begin to define the creators.

With the godlike powers of creation comes godlike responsibilities. The humans of Earth become a threat to the Dreens. Can the Dreens summon up the will to “erase” the Earth, to wipe out the human race? Or will the humans, with a bit of Dreen prodding, wipe themselves out with nuclear war?

There are many deft touches throughout the story. The human “hero” of the story, Lutt Hanson Jr., is merged with a Dreen juvenile delinquent, Ryll. Such human-alien combinations have been a staple of science fiction for generations, but the merger--sometimes cooperative, more often competitive--is handled very neatly.

Frank Herbert’s early days as a newspaperman show through clearly. And then there’s the irony of having a common herb of Earth act as a deadly narcotic to the Dreens.

I could not help feeling that both Herberts were trying to make a comment about the history of science fiction itself, especially when the Supreme Tax Collector tells her Dreen subjects that she is working “for the betterment of all and a return to the good old days of superb storytelling.”

Yet the novel lacks the resonances of the “Dune” volumes. Like the title and the dilemma of its protagonist, “Man of Two Worlds” is torn in different directions.

The Dreens, despite their powers, are forever fumbling and bumbling. Most of the humans don’t do much better. The novel is too serious to be truly funny, and too funny to be taken very seriously. One of the problems with collaboration is that the writers may enjoy each other so much that they lose sight of the work they are trying to produce. Like the good ship Pequod, a novel should have one master and one only.

Perhaps I am being too harsh. Perhaps the inevitable comparison with “Dune” and its sequels will harm this novel unfairly.

Of course, nothing can tarnish Frank Herbert’s place in the science-fiction firmament. It will be interesting to see if son Brian produces more science fiction, entirely in his own voice.