A new mode of naturalism has entered American writing, the world of the drifter and the dispossessed, sinewy studies of violence and injustice, but without the social comments or pleas of old. Hubert Selby, Edward Dorn, and Michael Rumaker are the most viable of these writers. Rumaker lacks the almost fanatical intensity of Selby and the hard-edged regional beauty of Dorn. His is a slighter, kinder temperament, and one of the discordant factors in these six longish tales is Rumaker's inability to keep his stringently depersonalized technique free of sentimentality or wispy bits of irony. This is very evident in ""The Bar"" and ""The Truck,"" gritty remembrances of urban delinquency with a set of hipsterized Dead End Kids: the talk and action is superbly persuasive and funny, but the endings somehow collapse into TV tears and bitterness. ""Exit 3,"" a savage glimpse of the nightmare loneliness of a drunken marine with dialogue so accurate it seems tape-recorded, and ""Gringos,"" a stunningly observed picture of two down-and-out Americans ambiguously cruising for sex and companionship in Mexico, are clearly the triumphs of Rumaker's collection. At his best, Rumaker's artistry is stingingly factual.