By Jane Sutton

GUANTANMO BAY U.S. NAVAL BASE, Cuba, Feb 12 (Reuters) - M icrophones that look like smoke detectors are installed in the huts where Guantanamo defendants meet to speak confidentially with their lawyers, the detention camp's chief legal adviser testified on Tuesday.

But the lawyer, Navy Captain Thomas Welsh, said conversations were not monitored when prisoners met in those huts for private talks with their lawyers or representatives from the International Committee of the Red Cross.

"We don't listen in," Welsh, who arrived at Guantanamo in 2011, told the war crimes court at the Guantanamo Bay U.S. Naval Base. "Under my watch, definitely, we don't listen in."

Welsh was called as a witness during a pretrial hearing for five prisoners facing capital charges of plotting the Sept. 11 hijacked aircraft attacks.

Defense lawyers contend that confidential conversations with their clients and among themselves are being monitored and possibly recorded at the Guantanamo Bay prison camp in Cuba.

Defendants have a legal right to consult their lawyers in private, and lawyers have an ethical duty to ensure the conversations are confidential.

The issue of who might be listening in has dominated this week's pretrial hearings for the alleged mastermind of the hijacked plane plot, Khalid Sheikh Mohammed, and four other captives accused of aiding and training the hijackers.

Welsh confirmed defense lawyers' suspicions that what appeared to be smoke detectors in the meeting huts were actually microphones that were "not readily noticeable."

He said he learned there was an audio monitoring capability in the huts in January 2012, when he saw a law enforcement official listening through earphones to an on-the-record meeting among prosecutors, defense lawyers and a detainee.

He called it a "proffer" meeting, suggesting the unidentified prisoner was working out a plea agreement.

INTELLIGENCE AGENTS CAN LISTEN IN

Welsh said he asked the detention camp commander about what he had seen and was told, "Don't worry, we do not monitor attorney-client meetings." But a recent search of his and his predecessors' email suggested some sort of meeting at the facilities had been monitored and recorded.

"If you need an affidavit from me that we did not keep sound recording I'd be happy to give it," a staff lawyer told Welsh's predecessor in a 2008 email.

Earlier on Tuesday, court Technology Director Maurice Elkins testified that U.S. intelligence agents receive a raw feed of everything picked up by the courtroom microphones.

He said stenographers receive the same feed and use commercial software and technology that allows them to isolate and record individual voices so they can prepare transcripts.

Elkins said he did not know whether intelligence agents had that capacity, or even who they were. He said he did not recall whether he had told defense attorneys prior to their clients' May 2012 arraignment that anyone other than the stenographers and interpreters were listening from outside the courtroom.

Defense lawyers said they only learned that intelligence agents were monitoring the courtroom proceedings on Jan. 28, when someone outside the courtroom cut the public audio feed under the mistaken belief that a secret had been disclosed.

Technicians have since dismantled the "kill switch" that let them cut the feed and altered microphones at the lawyers' tables to prevent live microphones at nearby tables from picking up whispered conversations. Instead of pushing a button to mute the microphones, lawyers must now push a button to activate them.

Defendants in the case could face the death penalty if convicted in the Guantanamo war crimes tribunal on charges that include terrorism, conspiring with al Qaeda, hijacking and murdering 2,976 people. This week's hearing was supposed to address whether the charges were properly filed, but have been sidetracked by the eavesdropping issue.

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