WASHINGTON — The Bush administration issued new rules Friday designed to allow the FBI to pursue potential national security threats with the same vigor and techniques used against common criminals. Civil libertarians said the guidelines will come at a cost to constitutional protections.

The rules, to take effect Dec. 1, are a roadmap to the FBI's transformation. The bureau made its reputation many decades ago by successfully pursuing bank robbers. The Justice Department says it wants to ensure that the FBI can now meet the biggest threats of the 21st century: national security and terrorism.

The roadmap consolidates once-separate rules for assessing threats and investigating traditional crimes and terrorism. They tell FBI agents what they can and can't do, including when to conduct surveillance, use informants and consider race or ethnicity in determining whether someone is a suspect.

While some changes were made from preliminary rules shown to reporters, lawmakers and public interest organizations, the alterations were not enough to silence critics who say the FBI will now be able to begin investigating people with no indication they did anything wrong.

Anticipating the criticism, Attorney General Michael Mukasey and FBI Director Robert Mueller issued a joint statement saying: "We are confident these guidelines will assist the FBI in carrying out its critical national security and foreign intelligence missions while also protecting privacy and civil liberties."

Sen. Patrick Leahy, D-Vt., chairman of the Senate Judiciary Committee, was not reassured.

"I am concerned that the guidelines continue the pattern of this administration of expanding authority to gather and use Americans' private information without protections for privacy or checks to prevent abuse and misuse," Leahy said.

Three Democrats on the House Judiciary Committee asked the department to postpone the effective date until a new president takes office in January and has an opportunity to review the procedures.

"Questions still remain about why there seems to be a rush to change these procedures in the last days of this administration," Reps. John Conyers of Michigan, Robert "Bobby" Scott of Virginia, and Jerrold Nadler of New York said in a joint statement.

The three said it was unclear whether the guidelines will result in FBI agents "monitoring the religious and political activities of innocent people."