NEW ORLEANS, Sept. 8 - Waters were receding across this flood-beaten city today as police officers began confiscating weapons, including legally registered firearms, from civilians in preparation for a mass forced evacuation of the residents still living here. . ."No civilians in New Orleans will be allowed to carry pistols, shotguns or other firearms, said P. Edwin Compass III, the superintendent of police. "Only law enforcement are allowed to have weapons," he said. . .But that order apparently does not apply to hundreds of security guards hired by businesses and some wealthy individuals to protect property. The guards, employees of private security companies like Blackwater, openly carry M-16's and other assault rifles. Mr. Compass said that he was aware of the private guards, but that the police had no plans to make them give up their weapons.