There is apparently no limit to the Bush administration's desire to invade Americans' privacy in the name of national security. According to members of Congress, Attorney General Michael Mukasey is preparing to give the F.B.I. broad new authority to investigate Americans - without any clear basis for suspicion that they are committing a crime. Opening the door to sweeping investigations of this kind would be an invitation to the government to spy on people based on their race, religion or political activities. Mr. Mukasey has not revealed the new guidelines. But according to senators whose staff have been given limited briefings, the rules may also authorize the F.B.I. to use an array of problematic investigative techniques. Among these are pretext interviews, in which agents do not honestly represent themselves while questioning a subject's neighbors and work colleagues. The F.B.I. has a long history of abusing its authority to spy on domestic groups, including civil rights and anti-war activists, and there is a real danger that the new rules would revive those dark days. Clearly, the Bush administration cannot be trusted to get the balance between law enforcement and civil liberties right. It has repeatedly engaged in improper and illegal domestic spying - notably in the National Security Agency's warrantless eavesdropping program. The F.B.I. and the White House no doubt want to push the changes through before a new president is elected. There is no reason to rush to adopt rules that have such important civil liberties implications.