One lawyer for Guantánamo detainees said he replaced his office telephone in Washington because of sounds that convinced him it had been bugged. Another lawyer who represents detainees said he sometimes had other lawyers call his corporate clients to foil any government eavesdroppers.

In interviews and a court filing Tuesday, lawyers for detainees at Guantánamo said they believed government agents had monitored their conversations. The assertions are the most specific to date by Guantánamo lawyers that officials may be violating legal principles that have generally kept government agents from eavesdropping on lawyers.

"I think they are listening to my telephone calls all the time," said John A. Chandler, a prominent lawyer in Atlanta and Army veteran who represents six Guantánamo detainees.

Several of the lawyers, including partners at large corporate law firms, said the concerns had changed the way they went about their work apart from Guantánamo cases. A lawyer in Chicago, H. Candace Gorman, said in an affidavit that she was no longer accepting new clients of any type because she could not assure them of confidentiality.

The new filing, by the Center for Constitutional Rights, came in a 2007 lawsuit under the Freedom of Information Act in which Guantánamo lawyers are seeking records to determine whether they have been targets of surveillance.

The Justice Department declined to comment Tuesday. But in a legal response in March, its lawyers said they could neither confirm nor deny that detainees' lawyers had been targets of such surveillance "because doing so would compromise the United States Intelligence Communities sources and methods."

Justice Department officials have said in the past that they had not used their terrorist surveillance powers to single out lawyers but that telephone "calls involving such persons would not be categorically excluded."

Since 2001, lawyers representing terrorism suspects not being held at Guantánamo have said they suspected government eavesdropping. Justice Department officials have said they intercepted such lawyers' conversations rarely and inadvertently.

But some detainees' lawyers say they believe there may be a comprehensive effort to monitor their communications at Guantánamo and elsewhere.

In the Tuesday filing in United States District Court in Manhattan, Thomas B. Wilner, a partner at Shearman & Sterling, said government officials insisting on anonymity had told him twice that he "should be careful in my electronic communications."

In addition to being a leading Guantánamo lawyer, Mr. Wilner is an international trade law specialist. "You need to be very careful in what you say on the telephone," he said in an interview.

Ms. Gorman's court filing said that during a visit to the Guantánamo naval base in Cuba, her military escort "referred in conversation to personal information about my family that I had not disclosed to him," leaving her to wonder how that information had been obtained.

Several of the lawyers said a program of surveillance would be consistent with obstacles they had encountered in representing detainees. In 2004, officials proposed "real-time monitoring" of lawyers' interviews with Guantánamo detainees.

A federal judge barred that, saying that listening to lawyers' meetings failed to recognize "the exceptional place in the legal system of the United States" for attorney-client communications.

Guantánamo officials say they monitor attorney-client meetings for the safety of lawyers with video cameras but that meeting areas are not wired for sound.

But several lawyers said their clients had told them that shortly after detainees met with lawyers, interrogators had asked the detainees about topics that had been discussed.

The Guantánamo spokeswoman, Cmdr. Pauline A. Storum, said interrogators were trained not to inquire about attorney-client meetings.

Shayana Kadidal, the lawyer at the Center for Constitutional Rights handling the freedom of information case, said there were many practical consequences of surveillance concerns. For example, he said, lawyers challenging the Bush administration's detention policies must travel worldwide for meetings with witnesses to avoid potential telephone or e-mail monitoring.

Jonathan Hafetz of the Brennan Center for Justice at New York University represents two brothers from Qatar, Jarallah al-Marri, who is held at Guantánamo, and Ali Saleh Kahlah al-Marri, who is held at the navy brig in Charleston, S.C., the only person on the American mainland known to be held as an enemy combatant.

After 16 months during which Ali al-Marri was held incommunicado, Mr. Hafetz was permitted to discuss the case with him. In 2006, Mr. Hafetz said, a guard commander told Mr. Marri that he had to speak in English during a conversation with his lawyer.

Mr. Hafetz wrote government officials asking whether the English-only requirement indicated that his conversations with his client were being monitored.

Mr. Hafetz said the commander of the brig later said there was no military surveillance. Mr. Hafetz said he never received a response about whether other agencies had listened to their conversations.

© 2008 The New York Times