The city attorney was directed to take whatever steps necessary to block the possible settlement in San Diego of convicted rapist Lawrence Singleton, whose parole has sparked a statewide furor over where he can live. Mayor Maureen O'Connor said council members gave City Atty. John Witt "carte blanche" in pursuing legal means designed to keep Singleton, 59, out of San Diego. Singleton served about eight years of a 14-year sentence for raping and mutilating a 15-year-old Northern California girl, whose forearms were hacked off with an ax. He was released from prison April 25, but state officials have been unable to find a city willing to accept the paroled convict. San Francisco and Contra Costa counties have obtained temporary restraining orders forbidding state corrections officials from placing Singleton in communities within their jurisdiction. Meanwhile, state officials are keeping Singleton's whereabouts secret.