SCIENCE-FICTION and fantasy writers expect young readers to suspend belief on one level or another. The best writers then take a giant step forward on their own and serve up the kind of mind-stretching rewards that give the genre such appeal. Several new titles offer some memorable adventures.
The Dragonbards, by Shirley Rousseau Murphy (Harper & Row, New York, $12.95, 249 pp., ages 12 and up), is the concluding volume of the author's generally acclaimed Dragonbards trilogy.
Although the book gets off to a bumpy start while Murphy brings new readers up to date with significant happenings from ``Nightpool'' and ``The Ivory Lyre,'' it soon assumes a harrowing narrative pace that builds to a grand, good-over-evil finale.
The evil Quazelzeg, lord of the dark and master of soulless ``unliving'' creatures, does his dastardly best to warp minds and break spirits. But he never really stands a chance against the virtuous young ``bards,'' their singing dragons, and hosts of helpful ``speaking animals.''
This is rollicking high fantasy decked out in magical powers and lyrical lyres reminiscent of Susan Cooper's award-winning ``The Dark Is Rising'' series.
In The Warriors of Taan, by Louise Lawrence (Harper & Row, New York, $12.95, 249 pp., ages 12 and up), crusader-like chieftains armed with crossbows and knives roar off to battle astride hairy yarrucks.
Outnumbered and outgunned by Outworlders equipped with rocket launchers and laser tanks, the warriors nevertheless prevail - thanks to a last-minute alliance forged with the peace-loving Sisterhood and birdlike Stonewraiths.
There's plenty of action in this futuristic saga. But the excitement is dulled by too many imposed messages about the virtues of womanly peace and love, and further weighted down with an ominous mood.
Plagues, and asides on communal birth control, of all things, do little to relieve the oppression. This will probably appeal to hard-core sci-fi fans, but it is a disappointing sequel to the author's evocative ``Moonwind.''
Sandwriter, by Monica Hughes (Henry Holt, New York, $12.95, 159 pp., ages 12 and up), introduces a similarly unfamiliar land - the desert island state of Roshan - that comes complete with heroic prince and princess, oases, mirages, and hooded figures flitting in and out of threatening sandstorms.
The author works hard to duplicate the kinds of believable settings and characters that made her Isis trilogy so popular, but keeps falling into one pretentious trap after another.
Declarations, such as ``The first step in wisdom is being aware that one knows nothing,'' have a hollow ring, and it's difficult to visualize the monstrous kroklyns and shabby lemas that comprise Roshan's beastly population. Still, this is a suspenseful tale.
The audience for Born Into Light, by Paul Samuel Jacobs (Scholastic, New York, $11.95, 149 pp., ages 11 and up), is more difficult to define, but may be just as devoted.
This is a quiet story, a look back to a rustic New England town of the early 1900s. Several feral children are discovered in the woods one spring day and subsequently adopted by a local family.
As they grow up with their human siblings, it becomes apparent that some unknown destiny awaits the children from the stars.
Although the resolution of their mission on earth may disturb younger readers, the author makes some touching points about the humanity of ordinary people involved in extraordinary events.
Stinker from Space, by Pamela Service (Scribner's, New York, $11.95, 83 pp., ages 8 to 12), is a mischievous lark of a sci-fi adventure, fine-tuned for voracious middle readers.
The premise requires a hyperspace suspension of belief, as Tsynq Yr, a crack extraterrestrial space pilot from the Sylon Confederacy, crash-lands his spaceship in the American Midwest and transfers his remarkable intelligence into the body of a passing skunk.
Nicknamed ``Stinker'' by the two youngsters who agree to help him hijack a space shuttle for his return home, Tsynq Yr spends his time browsing through NASA publications and scarfing up Chocolate Peanut Nuggets.
Ridiculous as it sounds, it works - thanks to the author's whimsical broad brush and clear attention to detail.