Military authorities have taken unusual steps to protect evidence in an espionage investigation at the Guantanamo Bay (searchprison camp, including classifying routine court documents and forcing visiting reporters to promise in writing not to ask about the case.

Air Force officers tried to close to the public a preliminary hearing for Senior Airman Ahmad I. al-Halabi (search), an Air Force translator facing 32 charges including espionage. His lawyers challenged the closure in the Air Force Court of Criminal Appeals, and the judges agreed to close only parts of the hearing that dealt with classified information.

Court staff refused to give out copies of the ruling, relying on Air Force officials to do so. The copies the Air Force released have signatures of court officials and telephone numbers of al-Halabi's defense lawyers blacked out.

The recommendations of the officer who presided over that hearing, Col. Anne Burman, also are classified. Reporters traveling to the prison camp in Cuba this week were required to sign a pledge not to ask questions about the investigation.

"It looks like it's going to be a fight from here until the end to keep this an open process," Maj. James Key III, one of al-Halabi's lawyers, said Tuesday.

Some secrecy is to be expected in the military's most high-profile espionage (search) case in more than a decade. Military law experts say the Pentagon has gone to extreme lengths, however, to protect secrets in the cases of al-Halabi and the Army captain and civilian translator arrested on suspicion of espionage at the prison.

"The court clerk's signature is not a secret. Why would they black it out in this case? I can't understand that," said Kevin Barry, a Virginia lawyer who is a military law expert and former Coast Guard appeals court judge.

"There does appear to be an effort with regard to anything having to do with Guantanamo Bay to reveal less rather than more," Barry said.

Unusual secrecy has shrouded the main military prison for suspected terrorists since before the first prisoners arrived in 2002. Even the number of inmates at the base in Cuba is classified -- authorities will say only that about 660 suspected members of the Al Qaeda network and Taliban, former rulers of Afghanistan, are held there.

This week, the form military officials made reporters who traveled to the base sign said they could not ask questions about "ongoing operations, future operations or investigations that are pending." The military had not insisted upon such ground rules in the past.

The Air Force did not announce al-Halabi's July 23 arrest until two months afterward, when reporters learned about it from Pentagon sources. Al-Halabi, a naturalized U.S. citizen who worked as an Arabic translator at the prison camp, is accused of collecting secrets about the base and messages from prisoners with plans to transmit them to an unspecified enemy in his native Syria.

The most serious charges against al-Halabi carry a possible death sentence upon conviction.

The admission of al-Halabi's arrest came after news broke of the Sept. 10 arrest of Army Capt. Yousef Yee (search), a Muslim chaplain at Guantanamo Bay. Yee has not been charged.

Military officials have said they wanted to keep the arrests secret to protect an investigation of possible security breaches at Guantanamo Bay. At least one other member of the military, who is in the Navy, is being watched, Pentagon officials have said.

Federal agents also arrested a civilian translator at the base, Ahmed Mehalba (search), last month for allegedly bringing Guantanamo Bay secrets with him on a flight to the United States from his native Egypt.

Mehalba faces charges in federal court, where most high-profile spy cases have been handled. Al-Halabi and Yee are in the military justice system, where espionage cases are more rare, although not unique.

Before a court-martial, a military defendant gets an "Article 32" hearing, similar to arraignment in civilian courts, after which the hearing officer sends a report to the accused's commander. The commander decides whether to impanel a court-martial or order a lesser form of military discipline.

Brig. Gen. Bradley S. Baker, al-Halabi's commander, had closed his "Article 32" hearing, saying "virtually all of the evidence presented during this Article 32 hearing can compromise current ongoing investigations that are of concern to national security."

Al-Halabi's lawyers objected, arguing that military court hearings, like federal court proceedings, should be closed only when absolutely necessary. The Air Force appeals court order then issued its order closing only hearings dealing with classified information.

The hearing was last month at Vandenberg Air Force Base, Calif., where al-Halabi has been held, and most of it was closed, attorney Key said. Some of al-Halabi's relatives attended the open portions, mostly involving testimony by the relatives, Key said. No reporters were there.

Military law allows court proceedings to be closed to protect government secrets and vulnerable witnesses such as children.