Latest book in the 'Dune' series lives up to Frank Herbert's tradition of good sci-fi storytelling; God Emperor of Dune, by Frank Herbert. New York: G. P. Putnam's Sons. $12.95.

Picture an entire world like the Sahara. The water is so precious there that the native people end their lives in special "still suits" which capture the water in their perspiration. They also ride the giant worms that live in the burning sands of the planet Arrakis, better known as Dune.

This planet is the setting of Frank Herbert's Dune series, which encompasses hundreds of worlds and a number of human and scarcely human cultures.

At its best, science fiction combines the breadth of imagination, of fantasy, with the disciplined logic of science and the depth of characterization of mainstream fiction. The Dune books offer one of the best examples of the fact that science fiction has come of age.

In the initial book, "Dune," Mr. Herbert artfully presented a universe in which mankind has spread throughout hundreds of planets to create a giant empire. At its core was a decadent oligarchy. As it grew, the stresses became increasingly difficult, and the empire verged on collapse.

The emperor and his vast bureaucracy could only cling to their powers because of the plant Dune, whose inhabitants were the fiercest soldiers in the empire. Even more important, its sandworms produced a powerful drug called melange, which could enhance an individual's parapsychological abilities, essential for piloting spaceships through interstellar space.

Among those who depended on this drug was a group of women, the Bene Gesserit , who for generations had been conducting a selective-breeding program. They used this substance to call forth and utilize the memories of all the females in the group. The objective of their eugenic program is to endow a male with this ability. They achieve their goal one generation early and in uncontrolled circumstances.

The result is Paul Atreides. Possessed not only of ancestral memories but unusually strong powers of precognition, Paul breaks with the Bene Gesserit and, by apparently sacrificing his life, destroys the empire by igniting a holy war that sweeps the galaxy.

The next two books, 'Dune Messiah' and 'Children of Dune," chronicle the Islamic-like religion that arises in the wake of the empire and holds the opposing factions in check.

Paul's twin children possess his gifts in even greater degree.Unless they make an almost unimaginable sacrifice, they realize, mankind will totally annihilate itself. On his daughter's part, this becomes the sacrifice of her life. But his son, Leto, faces an even more difficult challenge. He must give up his humanity.

Leto allows himself to become part sandworm. This makes him virtually indestructible and almost immortal. He assumes the role of "God Emperor" for several thousand years until humanity evolves to the point where it is mature enough not to destroy itself with the tremendous power at its finger tips. "Children of Dune" ended with this transformation. The fourth and newly released volume, "God Emperor of Dune," takes place 3,500 years after Book 3, at the end of Leto's reign. It is essentially a portrait of Leto, who is paradoxically both more and less than human.

Unlike some other series, the Dune books must be read in sequence. For those who have not read the original Dune trilogy, or, at the very least, the original volume, "God Emperor . . ." would be perplexing rather than pleasurable.

This latest book lives up to the Dune tradition and adds considerabl e richness to Herbert's world: