'LOT 97,' the auctioneer announced, 'a boy.' So begins Robert Heinlein's Citizen of the Galaxy, perhaps his best juvenile science fiction novel -- and a model for the way science fiction treats its favorite theme: the passage of the hero (or heroine) from childhood to maturity, from naivete to responsibility, from innocence to experience.

Thorby first appears as a rebellious young orphan in a galaxy-wide empire. In the course of the novel he will "try out" various life styles: slave, beggar, space trader, soldier, businessman. In each trade he learns useful skills and undergoes thrilling adventures, but whatever his condition, Thorby's actions are primarily governed by his hatred of domination, of anything that inhibits his freedom. Because of his early experience as a slave, he feels that no one should have authority over another. This is the novel's most obvious leitmotif. But there is a subtext, intimately related to the main theme: Thorby's unconscious search for a family. But how does one match the obligations inherent in family life against the claims of individual freedom? The novel revolves around the confrontation of these two conflicting philosophies: duty to self versus the authority of others. It is a conflict familiar to every child.

Most particularly, Heinlein treats in detail those family-like circumstances that require Thorby to give up some of his freedom and bow to the will of others. Thorby learns to obey the beggar he calls "Pop" out of love and from him he learns ethics; he follows the rules of a trading clan and acquires social skills; he becomes a good soldier out of admiration of the military and masters its manly virtues. Ultimately, Thorby rejects his genetically "real" but ultimately false family, and becomes his own man: the head of a huge enterprise that employs its resources to combat galactic slavery. Heinlein emphasizes that Thorby ends, in fact, as he began: as a slave, but this time to work of his own choosing. The boy, now a young man, has learned to subordinate some of his liberty to a cause he values. In short the novel demonstrates the need to balance freedom with obligation and responsibility. Thorby has grown up.

OF COURSE, growing up is to children's books what falling in love is to adult books. Just as many grownup novels end with a marriage (or nowadays a remarriage), so kids' books often conclude with the child's entry into adulthood. Indeed, follow the hero or heroine past that stage and you no longer have a book for children. In science fiction this maturation theme often grows to encompass mankind itself. The human race may be merely in its infancy or youth, as Arthur C. Clarke's Childhood's End proclaims directly in its title; and as Theodore Sturgeon's remarkable More Than Human suggests more obliquely. Both these novels look at the next step in the evolution of humanity, and both focus on children.

So too does the classic and exceedingly influential Slan by A.E. Van Vogt. A young boy, Jommy, finds himself an enemy of society because he has a special gift -- telepathy -- revealed by little antenna-like appendages on his skull, something like those of My Favorite Martian. Jommy longs for love and a place in his society, but is rejected by the normal people, indeed he is feared and hunted. Ultimately, however, he discovers that some of those he thought enemies are in fact allies; and in the end he joins them in a mission to transform his world. This schema, and variations on it, recurs countless times in science fiction, especially that intended for children. A young person feels out of place, longs to belong, is rejected, goes off on his own, develops his special gifts and ultimately makes peace with himself and either saves his society or establishes a new and better one. This is in fact just the process of maturation that all of us endure, feeling our way through life, trying to realize whatever special talents we may possess, and hoping to find a place for them in the world. Ultimately, too, we join with at least some of our erstwhile enemies.

The appeal of this kind of story is clear: every kid feels, deep in his heart, insecure and out of place, that he is unlike his classmates, that he is virtually -- to adopt a title from a recent collection of sf stories -- a Young Mutant. The sf novels that treat this theme teach tolerance and understanding of people's differences, repeatedly showing, as do fairy tales and other branches of fantasy, that apparent weakness may become a source of strength and power. The great lesson is that learned by Meg in in Madeleine L'Engle's A rinkle in Time: in one's differentness lies one's true self.

BUT UNUSUAL twists to this theme do occur. In The White Mountains. John Christopher portrays the passage to adulthood as a betrayal of boyhood. After capping -- a kind of confirmation or bar mitzvah -- boys become men, but they also become different: docile, more regular in their habits, distant, less rambunctuous and daring. Of course, in this novel, "capping" is a kind of alien brainwashing, one which suggests what adults look like to children -- staid, unadventurous souls. So in a neat twist, in Christopher's world, the rite of passage is something to avoid rather than undergo.

Though rites of passage and alienation appear in all children's literature, science fiction by its very formulaic character -- its closeness to myth, allegory and symbolism, its inherent tendency to offer a moral lesson -- may gain in impact what it loses in subtlety, often being brighter and bolder in its effects than more sophisticated and realistic fiction. The real world always confuses issues; but in an imagined place, on another planet or in another time, a theme or idea can be established without distraction and examined in a kind of controlled environment. Fantasy and fairy tales have taken advantage of this schematic approach for years.

Science fiction may also emphasize "growing up" in its various forms partly because the whole genre builds on belief in progress, on the possibility of scientific or social advancement, on conceptual breakthrough. The life of a child or teen-ager is one conceptual breakthrough after another. In its "moral" science fiction tends to advocate those qualities most Americans wish to foster in children: imagination, flexibility, tolerance, drive. These are often touted as virtues special to mankind, and as such are typically contrasted with the regimented hive cultures of so many alien societies. Anyone who's watched Star Trek reruns knows that each week the Enterprise triumphs because of, well, enterprise and imagination and kindness, qualities alien to the war-like, unfeeling, and highly regimented Klingons. Indeed, it is a commonplace that many of the sf novels of the '50s and '60s dealing with alien cultures are really about fictionalized communist or fascist societies, often reimagined as an insectoid or, as in the case of V, a reptilian race.

Because of its progressive -- indeed at times Pollyannaish -- spirit, a juvenile sf novel nearly always ends on a note of exhilaration (indeed, sometimes of complacent self-satisfaction). The hero triumphs. The universe which had seemed so confusing, powerful, and malevolent -- and children do see the world this way -- can be made subject to human intelligence, character, and ingenuity. An inspiring dream. Concomitant with this heroic vision, young-adult science fiction stresses again and again its image of the ideal man -- or woman. For at every stage in its history women have played major roles in science fiction. There have been female heroines like James Schmitz's marvelous Telzey; C.L Moore created the intrepid woman warrior Jirel of Joiry; authors from Mary Shelley through Leigh Brackett, to Ursula Le Guin, Joanna Russ, and Alice Sheldon (James Tiptree Jr.) have been crucial to science fiction's development. Similarly, John Brunner notes at the beginning of one of his novels that its hero bears a good old Earth name: Chang. And the protagonist of Childhood's End -- certainly among the half dozen classics of the '50s -- is black.

SUCH social awareness occurs chiefly, though not exclusively, in what is called "soft" or social science fiction, a form especially popular during gloomy adolescence and one that builds on the phrase "If this goes on . . ." Consider, for examples, 1984, Brave New World, We, The Iron Heel, Make Room, Make Room, The Martian Chronicles. All these novels are political dystopias, as much commentaries about the time in which they were written as they are visions of the future. Naturally most humorous or satirical sf also adopts this formula. One 1950s classic, Frederik Pohl and C.L. Kornbluth's The Space Merchants, describes an America run by advertising agencies.

"Hard" or technical sf, by contrast, prefers to deal with the classic children's question: "What if?" What if robots did everything? Read Jack Williamson's "With Folded Hands." What if a space ship approached the speed of light? Check out Poul Anderson's Tau Zero. What if a "planet" encircled its sun like a ring? Look for Larry Niven's Ringworld. Isaac Asimov wrote his most celebrated story, "Nightfall," -- once voted the best sf story of all time -- by simply building on a "what if" sentence from Emerson: "If the stars should appear but one night in a thousand years, how would men believe and adore."

In answering "what if" questions, hard sf writers focus intently on ideas and problems (rather than social conditions). For many people, the school years are just about the only time they have much interest in ideas. Children argue about everything, question everything. And this is again a reason why sf proves so appealing to the young: it is above all speculative fiction (a name that many prefer to science fiction). It is a literature of ideas (at times to the detriment of characterization or prose style.). Virtually all of H.G. Wells' short stories are idea stories; with little conversation and not much adventure, each is fueled by a provocative and at the time original notion: invisibility, creatures living on the sea bottom, weightlessness, the exchange of bodies, the fourth dimension. Consequently, the best time to read Wells is at 14, when just the thought of these ideas is entrancing.

This is not to say that ideas alone make a good sf story. The sf market is highly commercial and to succeed one must be able to tell a good tale, to entertain. This may lead to hack writing and conservative literary practices, but also to good, lively novels, written with competence and read with excitement. Grown-ups should be leery of depriving kids of such imaginative adventures as, say, Alfred Bester's The Stars My Destination or Frank Herbert's Dune; as sf writer William Tenn has observed, too many books carry such unappetizing titles as "A First Book About Floors for Boys and Girls." And as C.S. Lewis once noted, we mustn't allow the novel of manners to dictate standards to all fiction.

Happily, within science fiction there are books as simple as Daniel Pinkwater's zany Fat Men from Space and as intricate and highly wrought as Olaf Stapledon's Last and First Men or Gene Wolfe's Proustian tetralogy The Book of the Nw Sun. Growing up, at least with such books as these, can be quite an adventure.