Fantasy journey for all ages; Dustland, by Virginia Hamilton, New York: Greenwillow. $8.95.

Set aside your preconceptions; forget your notions of genrus; put "Dustland" in the hands of a reading child who knows and cares nothing about literary categories. Then read it yourself.

Virginia Hamilton is a writer of rare depth and range. Her subjects, her stories, her style, continue to press forward and away from what she has written before. "Dustland" is an exception only because it follows "Justice and her Brothers" and ought to be read as part of the Justice cycle.

Dustland is a place -- or is it simply the future? -- to which Justice and her twin brothers and their friend travel in their minds. The four children, each endowed with extrasensory power, can only move as a unit from home and the present to Dustland. Their mutual need is a blessing and a burden -- as are all intense relationships, all commitments.

In Dustland, nothing the children have previously known appears applicable to the strange life forms they encounter. the arid, choking, nearly featureless world means nothing if the four children cannot bring to it, along with their uncanny intelligence, a capacity to feel and care.

Dustland's inhabitants are few: the almost human Slakers, whose tortured thirst and perpetual quest for the end of Dustland are the basic conditions of their existence; and Miacis, a doglike creature who discovers through Justice the gift of language. Thomas, the illusionist who can create such compelling images that the others actualy feel them, carries in his nature and powers the terrible flaw of power unchecked and unrelated.

The struggle between Thomas and Justice, the recurring questions about the nature of reality, and the moral limits to which any individual may apply his or her unique powers, create a narrative tension in which character and idea become indivisible.

Young readers may be so spellbound with this book that they will taste the grit of Dustland for hours or days after the book is finished, but no one can close the book without a sense of being lifted, like the Slaker, beyond the dust into Hamilton's "enormous world of light."