A STRANGER IN THIS WORLD Stories by Kevin Canty (Doubleday: $20; 180 pp.) These are lean, bleak, powerful stories, which is not to say that they are lacking in tenderness. It just means that the characters who possess the least hint of vulnerability; genetic, financial, romantic, usually get squashed, like Judy in "Pretty Judy," a somehow disabled, sweet-dispositioned, very large young girl who is drawn into a sexual relationship with the boy next door. As in so many of these stories, however, the victim and the perpetrator both get hit by the shrapnel of some social or psychic explosion, some common 20th century malady like loneliness. In "The Victim," Tina, who suffers from a work-related repetitive motion disorder, just wants a normal life. Caught in a bad situation, every instinct she has left tells her not to take the next step. Canty, who lives in Montana and has had stories published in Esquire and Story, knows how to hurt us the way Flannery O'Connor did, and to scare us the way Dennis Johnson can.