PERHAPS the most exciting event in science fiction this month is the publication of Samuel R. Delany's new novel Stars in My Pocket Like Grains of Sand (Bantam, $16.95). It is the first half of what the author calls a "diptych," but it stands well on its own, both as a story of complex human relationships and as a tour- de-force of novelistic structure.

Delany has not written a science fiction novel for almost 10 years. He first rose to prominence with such novels as Babel-17 and Nova, works that superimposed, upon the old clich,e-prone space opera plots, dazzling new linguistic techniques. His gargantuan Dhalgren, over a thousand pages of recursive, dense writing, was a kind of Rubicon for him, and was the most vehemently debated science fiction novel of the mid-'70s. ditionalists condemned the novel's apparent lack of plot and what they perceived as murky self- indulgence. His next novel, Triton, was an uneasy compromise between the new Delany and the old; there followed a series of works of literary criticism, heavily influenced by semiotics and infiltrated with jargon, sometimes undigested. Then came a fantasy series set in the universe of Neveryon, which took the trappings of sword-and-sorcery and lampooned them with such lofty humor that few saw the jokes.

But the novel in hand marks a return to science fiction . . . to the galaxy-busting universes with which Delany first made his name. The tightly controlled plotting is back. What's new is that he has distilled his decade of experimentation and critical soul-searching and finally made it all work. This is an astonishing new Delany, more richly textured, smoother, more colorful than ever before -- and without the lumps of pretension that have disfigured other work of the past few years. This is one of Delany's finest novels, and as such must be considered one of the finest in science fiction.

Stars in My Pocket Like Grains of Sand is constructed as a series of set-pieces, and set- pieces within set-pieces. In the prologue we meet Rat Korga, a man reduced to zombie- like servitude by means of "radical anxiety termination," a sort of super-lobotomy that rids one forever of psychological problems -- and much else besides. By a bizarre coincidence, he is the only survivor of the destruction of his planet, a bleak and insignificant backworld.

The long central portion of the book chronicles roughly a day in the life of Marq Dyeth, an urbane citizen of the galaxy who inhabits an astonishingly complex universe. He is an industrial diplomat, and as such must deal constantly with planets with wildly differing societies and mores. There is a galactic information war going on, one of whose weapons is the destruction by massive cultural pollution of pristine planets. In Marq's overculture of humans and aliens, all sentient beings are known as "she" and all sex objects as "he"; and by this tiny shift in language Delany renders insecure all the reader's notions about how a culture should behave. To this world comes Rat Korga. He and Marq fall in love -- and their relationship literally sunders the fabric of galactic civilization.

That Delany actually brings off so hyperbolic a plot is astonishing. But more than that: there are enough novel images and weird concepts for a dozen books here, and they come at you relentlessly. Despite its length, this is not a flabby book. It is terse and muscular and explosive, and its author more in control than ever before. It is Delany's first true masterpiece. Jane Yolen

JANE YOLEN'S new novel, Cards of Grief (Ace paperback, $2.75), is another kind of first. For though the author has written over 70 children's books, this is he first adult title. It is derived from two earlier short stories anthologized in Elsewhere II and Tales of Wonder. The two tales are so disparate, both in their viewpoint character and in their narrative technique, that they seem irreconcilable by themselves; yet Yolen has made of them, by rewriting and adding material, a polished, seamless texture, a carefully crafted picture of an alien world.

It's a dreamlike book that in its few pages offers tantalizing glimpses of a bizarre, grief- haunted culture. The story is not unfamiliar: it is, like Stars in My Pocket, a tale of cultural pollution. But where Delany's is a pyrotechnic display, Yolen's book is a delicate thing of muted colors and refined emotions. While the premise is clearly science-fictional (we have an anthropological expedition from earth whose observation -- and miscegenation with -- the alien society cannot help but alter it irrevocably) the milieu is clearly that of fantasy.

On L'Lal'lor, the Planet of Grievers, timeis not perceived in human terms; the narrative flow of the novel is therefore recursive. The story concerns Lina-Lania, a master griever, from her apprenticeship and clumsy youthful attempts at decorating her "tables of grief" to her love for an earthman (in a society that does not possess the concept of love) and the beginning of the disintegration of that society. It's a cruel society; the rulers are not above having the heroine's relatives killed off in order to refine her grief and the profundity of her performance in the formalized grieving which is the planet's most important esthetic experience. It's a society where men, fertile for only a brief period in their lives, play a Byzantine role, and women rule. The details of the culture are worked out with an anthropologist's precision, and it would be an enviable construct in the most "hard-science" of sf novels. It is the preoccupation with absolutes -- with the nature of love -- that tips the into the genre of fantasy, and Ace has packaged it as such.

Jane Yolen's prose has grace and magic; when the time comes for hieratic passages, such as the quotes from the planet's mythology, she does not become at all stilted, but charges the lines with sensuous music. It is all too brief a novel; others could have created at least a trilogy from the material presented here. The power to distill, to concentrate the breakdown of a whole planet into a few images, is one of the greatest of Jane Yolen's considerable gifts. We must rejoice that she has decided to enter the field of books for adults; and even more, that she has not abandoned the childlike sensibility that is her strength. Jack Vance

UNLIKE THE first two authors under review, Jack Vance does not break into fresh terrain with his novel Rhialto the Marvelous (Baen Books, $12.95). Perhaps that is because he has already found, refined and mastered one of the most singular voices in science fiction. In this new novel, set in the highly colorful and popular milieu of his Dying Earth series, he gives us more of the same -- quirky descriptions, eccentric characters, convoluted plots that revolve on arcane intricacies of his Machiavellian, magic-dominated society.

The story itself -- the tale of a magical plot against the great magician Rhialto -- is a delight, but it is the trappings of the story that make the novel vintage Vance: the intricacy of the descriptions, the archness of tone. This passage, from the opening, could be by no other author:

"An insect settled upon the leaf of a nearby aspen tree; Rhialto took careful note of the angle at which it crooked its legs and the myriad red glints in its bulging eyes. Interesting and significant, thought Rhialto.

"After absorbing the insect's full import . . . "

Always inventive, never predictable, this book should be savored slowly. Powers and Adams

TWO MORE offerings may be noted this month: firs a new book by Tim Powers, Dinner at Deviant's Palace (Ace paperback, $2.95). This book was actually written before his highly acclaimed The Anubis Gates, a baroque time travel story with occult overtones which showed a virtuoso ability to handle wildly disparate plot elements. If Dinner, set in a futuristic and horrific L.A. and chronicling Greg Ravish's attempts to rescue his beloved from a particularly insidious cult, seems to speak less in that indivual voice familiar from The Anubis Gates, it should be noted that Powers was at that time heavily under the influence of the late Philip K. Dick. Stylistic echoes abound. But Dinner at Deviant's Palace is certainly worth reading, and its author is likely to become one of the most prominent figures in the field.

Douglas Adams' So Long, and Thanks for All the Fish (Harmony Books, $12.95) bills itself as "the fourth book in the Hitchhiker's Trilogy.) Fans of the sidesplitting series and of the television show, something of a cult object in some circles, are doubtless already standing in line to buy this book. To its credit, it is actually one of the funniest of the four volumes, as inventive and zany as the first (The Hitchhiker's Guide to the Galaxy) and certainly far more entertaining than its most recent, rather tiresome predecessor, Life, the Universe, and Everything. For those unfamiliar with the ever-expanding trilogy, this is as good a place to start as any. Adams' humor is incisive and unerring, and seems to be based on a deep knowledge of and love for science fiction -- something rare in humorists. I recommend it.

Somtow Sucharitkul is the author of 10 science fiction and fantasy titles, most recently "Utopia Hunters."