A former Arabic translator at the American-run prison camp at Guantanamo Bay has agreed to plead guilty to charges stemming from his alleged removal of classified information from the base.

Ahmed Mehalba, 32, was arrested in September 2003 at Logan Airport in Boston as he returned from a trip to Egypt. Authorities accused Mr. Mehalba, who was born in Egypt and naturalized as an American citizen in 1999, of carrying a compact disc containing 368 classified documents. A federal grand jury later charged him with one count of retaining classified information without permission and two counts of lying to a Customs agent about the matter.

Mr. Mehalba initially pleaded not guilty to the charges. However, his attorneys confirmed this week that he is scheduled to change his plea Monday afternoon in federal court in Boston.

“It’s docketed as a change-of-plea hearing,” said an attorney for Mr. Mehalba, Michael Andrews.

Mr. Andrews declined to say exactly what charges his client would plead guilty to or what concessions the government had offered. “Usually people don’t plead without getting some kind of benefit,” the lawyer observed.

A spokeswoman for the prosecutors declined to comment on the development.

Mr. Mehalba’s guilty plea could mark the final chapter in a high-profile investigation into a possible espionage ring at Guantanamo Bay, an American military installation that houses hundreds of prisoners captured as part of the war on terror.

In July 2003, military investigators arrested an Air Force supply clerk who worked as an Arabic translator at Guantanamo, Senior Airman Ahmad Al Halabi. He was charged with attempted espionage, possibly for Syria, and was also accused of removing classified detainee rosters and letters from the base.

In September 2003, a Muslim chaplain at Guantanamo, Army Captain James Yousef Yee, was arrested. The military initially told him he was being held on suspicion of espionage or treason. Eventually, Captain Yee was charged with lesser crimes, including mishandling classified documents and disobeying orders.

Mr. Mehalba, who worked at Guantanamo as a contract linguist provided by Titan Corporation, was never charged with espionage, but one of the prosecutors who has filed briefs in his case is from the Justice Department’s counterespionage section. Mr. Mehalba worked at the base for about eight months before he was detained in Boston.

All of the men denied wrongdoing.

The string of arrests involving Muslims who worshipped together at Guantanamo raised fears of a grave security breach at the base. Commanders ordered an immediate review of security procedures at the facility.

Over time, however, the cases against the men fizzled. Captain Yee was charged with adultery and storing pornography on a government computer. A hearing about a sexual affair he allegedly engaged in at Guantanamo led to a bizarre public confrontation between his alleged mistress and his wife outside a military courtroom. No evidence of espionage was produced. Citing concerns about disclosures of sensitive security information as the case proceeded, the military ultimately dropped all charges against Captain Yee and he agreed to leave the Army.

Days before Al Halabi’s court martial was to begin, prosecutors disclosed that military classification experts had determined that only one of the documents he removed from the base was actually classified. Defense attorneys also found a witness who said that investigators drank beer and staged photographs as they handled key evidence in the case.

Last September, Al Halabi pleaded guilty to mishandling classified materials, taking photographs in violation of orders, and lying to investigators. He was given a bad-conduct discharge from the military. The initial espionage charges, which could have brought him life in prison, were dropped.

Mr. Mehalba’s arrest also drew considerable attention. News reports noted that he once applied, unsuccessfully, for a security guard job at the same airport where he was arrested.

He also worked as a cab driver in Boston, like a number of Islamic radicals who have been suspected of links to terrorism.

While those facts seemed suspicious, some observers said it was doubtful that someone engaged in espionage for radicals abroad would try to smuggle secrets into America. Mr. Mehalba’s attorneys also produced glowing recommendations he received for his work at Guantanamo. His lawyers said his journey to Egypt was to visit family. He met a woman during the trip and married her, they said.

After the initial flurry of coverage, Mr. Mehalba’s case lumbered on without much drama and with little attention from the press. He has spent more than 15 months in custody awaiting trial. His attorneys have repeatedly asked that he be released into a halfway house. A federal magistrate and judge have rejected those requests.

Even if Mr. Mehalba’s guilty plea is accepted on Monday, and he gets no additional prison term, he will have served more jail time than any other American accused of Guantanamo-related misconduct.

Prosecutors have never publicly described in detail the classified information Mr. Mehalba allegedly had among the compact disks in his luggage. However, in a ruling last September denying Mr. Mehalba’s release, Judge Douglas Woodlock wrote, “It should have been apparent the materials were plainly not properly the subject of transport or handling in the fashion that the defendant is alleged to have undertaken.”

Because of personnel shortages, some linguists were sent to Guantanamo before their background checks were complete. Military officials said the short-circuiting of the clearance process may have contributed to some of the security breaches.

Defense attorneys have accused the military of mounting a witch-hunt against Guantanamo personnel who raised concerns about the treatment of detainees. Islamic groups have also alleged that Muslims were targeted for special scrutiny by their superiors. Spokespeople for the Pentagon have denied those claims.

Soon after the initial publicity about a suspected spy ring at Guantanamo, the military charged a non-Muslim Army intelligence reservist, Army Colonel Jackie Farr, with mishandling classified information and making a false statement to investigators. Last August, a commander dropped the criminal case and quietly meted out an administrative punishment to Colonel Farr, who was a top interrogator at the base. Officials have declined to describe his punishment in detail.

Earlier this week, the military announced it has opened a formal investigation into another type of alleged misconduct at Guantanamo: the reported abuse of prisoners by American military personnel.