FRANK HERBERT is probably the only major science fiction writer to have attained that status on the basis of a single novel.

Throughout the '50s and '60s he was known primarily as a rather undistinguished writer of short stories for various science fiction magazines. The publication of Dune in 1965, however, established Herbert as a major name in the field. Dune quickly went on to become a best seller and one of the most notable of all sf books (although surprisingly, not one yet subjected to extensive literary analysis).

Although the trappings of Dune were those of science fiction, in substance and form the book resembled fantasy, and the Tolkien books of Middle Earth more than the standard classics of sf. The society of Arrakis represented feudalism on a grandiose scale; science and technology, while not quite nonexistent, were totally secondary to the metaphysical aspects of this desert planet and its vaguely Arabic culture.

Like Tolkien, Herbert showed himself to be a master word builder. He used a strong narrative -- a struggle for political control of Arrakis -- almost solely as framework for presenting the marvelous details of his creation (most memorably the giant sandworms, the mysterious Bene Gesserit sisterhood, and the Fremen, a desert people who use moisture suits to conserve their perspiration). His characters were not really memorable as individuals, but were vital components of the fascinating, waterless world in which they lived.

In the sequels Dune Messiah (1969) and through most of Children of Dune (1976), Herbert neglected the enrichment of his world in favor of lengthy enigmatic conversations, often about religion, human evolution or psionic abilities, all themes of the series. Only in the last few chapters of Children of Dune did the story again pick up in interest, as Leto Atreides, having discovered his inner powers, fights to gain control of an empire and makes his irreversible decision to start his slow transformation into something not quite human.

Now we have a fourth novel, God Emperor of Dune, set 3500 years after the close of the trilogy, well into the slow metamorphosis of Leto Atreides into an enormous sandworm.

Though God Emperor of Dune does not suffer from the authorial indulgences of the two previous books, readers hoping once again to experience a vision of the complex power and richness of Dune will be disappointed.

In God Emperor Herbert has a new, later Dune to create, one ruled by the virtually immortal, part-sandworm, part-human Leto. Although this novel is a pale reflection when compared to Dune, Lord Leto himself is one of the more original and awe-inspiring creations in science fiction. The most successful section of the novel occurs when Leto takes a young woman rebel, whom he hopes will come to understand and support his plans for the guidance of humanity, into the desert to teach her slowly about what it was like to live on Dune thousands of years before.

Perhaps Herbert may again write a book of the power and scope of Dune. But in the meantime his admirers will have to make do with books like God Emperor of Dune in which an occasional spark of the old brilliance shines through.

Two early works by Frank Herbert have just been reissued, The Green Brain (Gregg Press, $13.50) and The Worlds of Frank Herbert (Gregg Press, $13.50). The former is a novel published in 1966, directly after Dune, and is notable for an interesting and relatively believable corporate mind formed by mutated insects, and for rather quaint environmental theories. The other is a collection of nine short stories, and shows why Herbert has never been known for his short stories.