While it was unfolding in 1974, the Patricia Hearst kidnap saga, with its elements of generational revenge, ragtag class war, and Mansonesque cult madness, was dominated by the enigma of Hearst herself: When the 19-year-old heiress joined the ''cause'' of the Symbionese Liberation Army, those tin-pot-nihilist dregs-of-the-'60s radicals, did she become a machine-gun-toting revolutionary of her own accord, or had she been brainwashed? The question lingers in Robert Stone's Guerrilla: The Taking of Patty Hearst, a gripping documentary that uses voluminous period evidence unedited news footage, tape recordings of SLA leader Cinque's rants to brilliantly reconstruct the entire freak event. What the film reveals, however, is that the way the episode played out, moment to moment, in the newly technologized mass media now looks every bit as exotic as the mystery of how Patty Hearst became the poster child for Stockholm syndrome. The TV networks, parking thickets of cameras in front of the Hearst mansion, became an electronic message board for the SLA, erecting, in effect, the entire apparatus for the tabloidization of mainstream news culture. To watch the surveillance footage of Patty (I mean, Tania) robbing a San Francisco bank is to taste the chaos, the delusion, the unironic free insanity of the '70s.