WASHINGTON - Legal and civil rights groups predicted court challenges Friday to a new Justice Department rule that allows federal authorities to monitor communications between lawyers and some clients jailed in connection with terrorism investigations.

The Bush administration defended the rule as important to its campaign against terrorism and said the new powers would be used narrowly and cautiously.

"The attorney general has been exceptionally careful and FBI Director (Robert) Mueller very precise in direction they've given to the law enforcement community with regard to constitutional protections," Homeland Security Director Tom Ridge told reporters at a press conference Friday.

The rule applies to conversations and mail between jail inmates and lawyers when the head of a U.S. law enforcement or intelligence agency has a "reasonable suspicion" that the inmate is using the contacts to "facilitate acts of terrorism" or violence.

According to Justice Department spokeswoman Mindy Tucker, the measure currently affects 13 federal inmates. None of the 13 subject to monitoring were taken into custody as a result of investigations into the Sept. 11 attacks, she said.

"This is a breathtaking violation of civil liberties," said Elizabeth Alexander, director of the National Prison Project, which represents prisoners for the American Civil Liberties Union. "I am absolutely certain that if the government doesn't back down on this, litigation will immediately follow."

Alexander said a lawyer could file a lawsuit claiming a breach of professional rights. A client could also file suit, she said.

The National Association of Criminal Defense Lawyers is looking for ways to challenge the rule, said the group's public affairs director, Dan Dodson. Association President Irwin Schwartz said it undermines the principle of attorney-client privilege.

"Rules and codes of professional responsibility are very clear: an attorney cannot communicate with a client when confidentiality is not assured," Schwartz said. "And there can be no effective representation without communication."

Sam Dash, a Georgetown University law professor who was counsel to the Senate Watergate Committee in the early 1970s, said Attorney General John Ashcroft is essentially trying to bypass an already-available option of getting a court order to do wiretaps or searches, even of lawyers when evidence warrants.

"It's basically lawless law enforcement," Dash said. "Unfortunately that's a throwback to an attitude at the time of Watergate." Dash said the rule could be blocked by a court order enjoining its enforcement.

The American Bar Association took the same view as Dash on Friday, saying that the rule is unnecessary and unconstitutional.

The rule "runs squarely afoul of the Fourth and Sixth Amendments to the Constitution," said Association President Robert A. Hirshon.

Under the rule Ashcroft implemented Oct. 30, the lawyer and client would be notified if their communications are to be monitored, unless a court order specifies otherwise. The team monitoring the communications will have no connection to the jailed client's case and conversations overheard cannot be used in court.

Georgetown University Law Professor Susan Low Bloch said the rule might be defensible if it carries enough safeguards and restraints.

"It's an extreme measure," Bloch said. "but these are extreme times."

The rule came under attack from Sen. Patrick Leahy, D-Vt., chairman of the Senate Judiciary Committee. Leahy said in a letter to Ashcroft Friday that he had no warning of the measure.

"I am deeply troubled at what appears to be an executive effort to exercise new powers without judicial scrutiny or statutory authorization," Leahy wrote. "As fellow prosecutors, you and I both know that the rule of law is essential to our American freedoms, and the right to a lawyer with whom one can communicate candidly and effectively is essential to the adversary process by which the rule of law operates in America."

Leahy submitted a list of seven detailed questions about the legal basis, timing and expected use of the rule, seeking responses by Monday.