Science fiction: heavy on adventure; Warriors of the Wasteland, by Douglas Hill. New York: Atheneum. 130 pp. $9.95.

A sequel to ''The Huntsman,'' Douglas Hill's latest novel will delight those science fiction fans who prefer their fare spiced with a heavy dose of adventure.

Continuing the search for his foster sister captured by the alien ''Slavers'' who now rule earth, Finn Ferral faces the barren Wastelands. In this harsh desert, he and his trusty companion Baer - a member of the Bloodkin, a race descended from humans - learn that the Slavers have sent in pursuit of them an evil master warrior named the Claw. Finn also finds himself thrown in with a cunning band of humans - descended from a group of people known as Indians (in the Forgotten Time before mankind incinerated itself with its own massive weapons) - who fiercely fight the Slavers in skirmish after skirmish.

The dilemma the independent Finn must face is whether to join the warrior band in what is clearly a futile fight to overthrow the alien tyranny, or to stay clear of any such ties and continue his fight alone.

As one might guess from the title, there is violence - of the battlefield variety. But there's a bit of a moral element to the book, not to mention a casually nonsexist attitude that's refreshing. And for younger ''Star Wars'' fans not yet ready for Isaac Asimov, it provides an enjoyable introduction to the literary side of the genre.