With a military espionage trial against a former Air Force translator at the U.S. military prison in Guantanamo Bay, Cuba, set to begin Tuesday, the Air Force has backed off from much of the evidence against him.

In a statement last week, the Air Force acknowledged that only one of the more than 200 documents it had accused Senior Airman Ahmad al Halabi of plotting to smuggle into Syria was classified.

The concession is the latest government retrenchment in a series of cases that last year led investigators to suspect a possible spy ring at the prison for alleged al Qaeda and Taliban fighters, and resulted in the arrests of two U.S. servicemen and a contract translator, all of them Muslim.

Earlier this year, the government dropped all charges against Capt. James Yee, a Muslim Army chaplain. He had been threatened with the death penalty for sedition and espionage when he was arrested in 2003.

A third man, Ahmed Fathy Mehalba, a former civilian translator at Guantanamo Bay, faces trial in a Boston federal court. Mehalba, a naturalized U.S. citizen of Egyptian descent, was arrested a year ago at Boston's Logan International Airport and was charged with illegally transporting computer discs containing classified information about the detention facility and lying about it to officials.

Halabi was arrested July 23, 2003, and was jailed on a military base until May. He still faces 16 counts of attempted espionage, lying to investigators and disobeying orders, with the spy charge carrying a possible maximum sentence of life in prison.

But after the Air Force's admission, defense attorneys have moved for the dismissal of the espionage charges against Halabi. They say the collapse of the Yee prosecution and the government's about-face on the Halabi documents show that the case against him reflects anti-Muslim bias, not the existence of an espionage ring.

"This ice cube is melting quickly," said Eugene Fidell, a Washington civilian attorney who represented Yee.

Nevertheless, the government plans to press ahead with a court-martial of Halabi, with pretrial hearings set to begin at Travis Air Force Base in California on Tuesday.

"We asked them if they will continue to prosecute based on the one document, and they said yes," Halabi's civilian defense lawyer, Donald G. Rehkopf Jr., said in an interview.

In the statement, the Air Force said that its admission that most of the allegedly secret documents were not classified "relates to some, but not all of the charges against SrA al Halabi." Citing Halabi's right to a fair and impartial court-martial, an Air Force spokeswoman at the base, Capt. Michele M. Tasista, said that prosecutors could not comment further.

Halabi, 25, is a naturalized U.S. citizen who immigrated as a teenager from Syria, a country that the State Department lists as a sponsor of terrorist groups.

Before he was transferred to Guantanamo Bay in November 2002, Halabi had worked as a supply clerk in California and Kuwait.

At Guantanamo, his main job was translating letters to and from the detainees.

Authorities accused him of attempting to give Syria more than 180 of those letters, plus a map of the base, flight schedules, intelligence documents and a roster of prisoners.

Among the evidence officials cited for the charge were Halabi's contacts with the Syrian Embassy in Washington and his purchase of a plane ticket to visit the Middle Eastern country in July 2003.

Halabi's attorneys maintain that their client had merely asked the Syrian Embassy for a routine entrance permit and that the purpose of his trip was to get married in his home country among relatives.

He had been authorized by his superiors to keep copies of the detainee correspondence on the hard drive of his laptop computer, defense lawyers say, because the base did not have enough computers of its own.

The government has never named the person or agency in Syria to whom Halabi was supposed to give the documents, defense lawyers say.

The defense also notes that one military investigator in the case was removed and charged with rape and sodomy against a child and a teenager, and separately with failing to safeguard classified information. A second investigator, the defense contends, is guilty of misconduct in the handling of evidence in the Halabi case.

Ahmad al Halabi is charged with attempted spying, lying, and disobeying orders.