Pentagon officials also said they were looking into newly public allegations that interrogators at the U.S. military prison at Guantanamo questioned detainees under the guise of being FBI agents.

The American Civil Liberties Union obtained and released e-mails that showed FBI officials disapproved of the practice and suggested the military interrogators were trying to take advantage of the rapport the FBI had established with some detainees.

Pentagon spokesman Bryan Whitman said such a technique was not on a list of interrogation methods approved by Defense Secretary Donald Rumsfeld. It was difficult to determine from the e-mails, however, whether it ''was permissible or not.'' Defense officials said it is permissible to impersonate a foreign national during interrogations.

The military operation at Guantanamo Bay has come under increased scrutiny as former prisoners have alleged they were tortured.

The Pentagon maintains it runs a humane operation there, and says all allegations of abuse are investigated.

Asked about Guantanamo at his news conference Monday, President Bush said, ''You've got to understand the dilemma we're in. These are people that got scooped up off a battlefield attempting to kill U.S. troops. And I want to make sure, before they're released, that they don't come back to kill again.''

Of the roughly 200 that have been released at least a dozen have returned to the battlefield, Navy Secretary Gordon England said.

The newest prisoner to face release would be the second to be freed under a military process instituted to help satisfy the Supreme Court's ruling during the summer that prisoners at Guantanamo could challenge their detentions through the U.S. court system.