GUANTANAMO BAY NAVAL STATION, Cuba – Nearly two dozen investigators are searching for possible security breaches at the U.S. prison for terror suspects, officials said Thursday at the camp where espionage charges have heightened tensions. Sources familiar with the investigation said two more arrests may be imminent.

Investigators from the Miami-based U.S. Southern Command reported to the island on Saturday and on Tuesday, the same day as five non U.S.-born interpreters contracted by the same company that employed an American translator who has been arrested.

Investigators will try to establish how a translator already under investigation got secret clearance and was allowed onto the base, and how a second translator managed to leave with classified information. In addition, a Muslim chaplain is under investigation after allegedly leaving with diagrams of the prison layout.

The translators, from San Diego-based Titan Corp., arrived as officials boosted security by closely monitoring e-mail messages, asking troops to report suspicious behavior, and postponing the assignment of another Muslim chaplain.

Army Maj. Gen. Geoffrey D. Miller, who commands the detention mission, said they also are increasing baggage checks and considering lie detector tests.

He thought Titan had done a good job but said its contract is under review: “They go through a very thorough screening process, but that contract is being reassessed.”

“I was surprised” by the arrests, Miller said, but would not discuss how security might have broken down.

Titan employed Ahmed F. Mehalba, an Arabic translator charged with lying to federal agents when he denied the compact disc he was carrying contained secret information from Guantanamo.

A second translator, Senior Airman Ahmad I. al-Halabi, was already under investigation for allegedly making anti-American statements before he arrived at Guantanamo. He is now charged with espionage and aiding the enemy.

Both translators say they are innocent.

Army Capt. Yousef Yee, the chaplain, is being held on suspicion of aiding the enemy.

Both military and civilian officials acknowledge part of the problem is finding qualified linguists for Guantanamo, where about 70 translators help 200 interrogators in 17 languages.

“They’re always looking for Arabic interpreters,” said Peter Peterson, an Iraqi-American translator who arrived Tuesday. “I believe in what I’m doing, though, and I believe in the mission.”

The Guantanamo detention mission began Jan. 11, 2002, as an impromptu operation with 20 shackled terror suspects locked behind crude chain-link cells. The prison camp — now an enclosed facility called Camp Delta — has grown to 660 detainees suspected of having links to al-Qaida’s terror network or Afghanistan’s ousted Taliban regime.

“You can have the most secure cells and an isolated military base, but if you don’t control the people who come onto the base, you have a serious problem,” Matt Levitt, a terrorism analyst and senior fellow at the Washington Institute, said by telephone.

Levitt said if there were three security breaches at Guantanamo it represented “a colossal intelligence failure.”

The prisoners, from 42 countries, are not allowed access to lawyers and none has been charged. At least three are teenagers. Defense Secretary Donald Rumsfeld has said they could be held until the war on terror ends. And construction workers said Thursday they have begun building a permanent concrete prison.

At the base, new leaflets warn troops to watch what they say.

Miller took over in November 2002 and quickly instituted a system of rewards for detainees who cooperated in interrogations, ranging from bottled water to being moved to a medium-security wing.

Miller has said the rewards system has yielded valuable information about terror cells and recruiting. “We have five times as much intelligence as we did during the same time last year,” he said Thursday.

But as restrictions eased, relationships reportedly grew between the detainees and their captors.

“Some of the men wrote to their families saying they had developed relationships with some of the camp personnel,” said Qatari lawyer Najeeb al-Nauimi, who is trying to get at least 90 detainees released to their native countries.

Investigators want to know how deep the relationships were, and whether translators could have misrepresented statements to protect detainees.

Miller said officials continue to exercise security precautions because “These (detainees) are still very bad people.”

Meanwhile the only independent group with access to the detainees, a team from the International Committee of the Red Cross was wrapping up its latest visit Thursday in meetings with U.S. officials.

The ICRC has urged the United States to abide by international conventions governing prisoners of war. International rights groups have said the indefinite detentions without charge, which have led to dozens of suicide attempts, are inhumane.

But Miller insisted Thursday that “There’s never been an issue with the ICRC about the humane treatment we give to the detainees.”