BOOK REVIEW : Science Fiction Merely Fantasy If Premise Upstages Characters : SHADOW HUNTER <i> by Will Baker</i> , Pocket Books $21, 373 pages

The word utopia has been around since 1551, when Thomas More published his fantasy of the same name portraying a society boasting “the beste state of a publyque weale.”

The word dystopia, utopia’s opposite, is of much more recent origin--so new, in fact, that you won’t find it in most dictionaries, even those updated within the last few years.

The belated arrival of a word describing anti-utopias comes as something of a surprise because modern literature has produced far more dystopias than utopias.

“Brave New World,” “1984,” “Fahrenheit 451,” “A Clockwork Orange,” all kinds of science fiction since the 1960s: This century’s writers have found more to fear from the future than to celebrate.

“Shadow Hunter” isn’t in the same league as the novels just mentioned, but Will Baker’s dystopia is generally convincing and contains one very scary, marginally plausible idea.

The year is 2131, and the world has been divided into two strictly defined hemispheres: the North, where most work has been taken over by machinery and life is largely escapist, and the South, a radioactive wasteland created by a nuclear war.

Politics remains an over-riding preoccupation in the NorthAm nation, yet the major tension is not international but domestic, as competing political parties attempt to deal with growing fears about the South. The South, many fear, is about to rise again, led by a sometimes cannibalistic, supposedly degenerate human subspecies called, disparagingly, the Ginks.

The frightening idea that sets “Shadow Hunter” in motion is Baker’s suggestion that non-human species, having suffered centuries of trauma at the hands of man, could have evolved cooperative strategies with which to battle their common enemy.

NorthAm’s Conservative government, which has championed “unplanned diversity” (and is obviously a twisted descendant of today’s environmental movement), is willing to gloss over reports of animal cooperation, but the rival Progressive party is terrified by it, believing that nature should be controlled and “improved” for the benefit of human society.

A major goal of the “Progs” is extermination of the Ginks, and they see the perfect opportunity with which to regain power and implement their platform when an absent-minded 13-year-old, Ronny Drager, falls into Gink hands in the course of a high-tech hunting expedition.

Ronny becomes a cause celebre , and it’s soon clear that the NorthAm government will stand or fall according to which party--or mercenary--rescues him.

Ronny, of course, is initially terrified at being kidnaped, but before long he finds that the Ginks (who call themselves “the Pobla” and humans “piksis”) bring out in him a spiritual power that had previously lain dormant. He encounters a teen-aged Gink named Tima, who was captured as a child and trained by NorthAm scientists and has returned to Gink lands for the first time as part of a risky, top-secret operation to recover Ronny.

The plot of “Shadow Hunter” is more complicated than this synopsis implies, but the complications add color and length to the novel rather than depth.

Baker, a professor of creative writing at UC Davis, thanks in the acknowledgments his decades of fiction workshop students for having “ignored my prejudices against the fantastical and outlandish products of the unshackled imagination and thus tempted me into writing such a book.”

Baker’s initial skepticism about fantasy fiction is, of course, on target.

“Shadow Hunter” is a good book in the fantasy genre, but it remains a genre novel because Baker’s characters play second fiddle to the environment their author has created for them.