The basic biological behavior in Quest for Fire has the bluntness of a nature documentary. The story, about cave men struggling heroically for survival, is punctuated with violence and sex that are unsettling and sometimes flatly offensive. But there is nothing scary or erotic about these passages; they are in the matter-of-fact vein of a zoological work like ''The Naked Ape,'' and indeed, author Desmond Morris was hired to create the prehistoric gestures of the characters, just as linguist Anthony Burgess created their lexicon of pre-Indo-European language. Over lunch recently, director Jean-Jacques Annaud (who won an Oscar for ''Black and White in Color'') explained that documentary-like realism was his goal, and that he was partly inspired by the opening of the classic film ''2001: A Space Odyssey,'' with its portrayal of simians about to become human. Annaud's vision lacks the resonance of Kubrick's in ''2001,'' however, and his hard physical approach may lose him much of the wide audience of all ages he would like to reach.