A longtime captive at the U.S. military prison in Guantanamo Bay, Cuba, will be sent home to his native country after a military tribunal there determined that he is not an enemy combatant, Navy Secretary Gordon R. England announced yesterday.

The decision ends nearly three years of incarceration for the man, who was picked up on the battlefields of Afghanistan.

England declined to provide details of the detainee's case, including his name and nationality, referring to an agreement with foreign countries not to release such information until a transfer home is completed. Pentagon officials, speaking on the condition of anonymity, said the detainee, who is not an Afghan national, was captured in January 2002 and held in a detention facility in Afghanistan for a few months before he was transferred to Cuba, where he has been incarcerated ever since.

Human rights advocates sharply criticized the government for the length of the detainee's incarceration.

"It should not take more than two years for the U.S. military to determine that we were holding someone who is apparently not an enemy combatant," American Civil Liberties Union executive director Anthony Romero said in a statement yesterday. "While this announcement is welcome, hundreds of so-called enemy combatants still languish in legal limbo at Guantanamo Bay. The government's assertion that it is entitled to lock people up indefinitely without any access to the courts violates our most basic notions of fundamental fairness."

The detainee is one of 55 inmates who have received a complete review under a program begun recently by the military to determine whether detainees should continue to be considered enemy combatants, England said. A Navy admiral who must approve the tribunal decisions has decided 30 cases so far -- ruling that 29 detainees are enemy combatants and that this one is not. More than 200 such tribunal cases are in various stages, England said.

The government has described the tribunals, which the Defense Department launched in response to a U.S. Supreme Court ruling that detainees are entitled to contest their incarcerations in federal courts, as a way of providing detainees a chance to present their cases for release. The detainees are not entitled to attorneys but can call witnesses and offer evidence.

"There is such a thing as better late than never, but I'd imagine that's cold comfort to this person," said Eugene R. Fidell, president of the National Institute of Military Justice. "It's good that this error has been noticed and this determination has been made, but it's one that should have been made literally years ago."

Pentagon officials have worried that releasing detainees without thorough review could prove deadly to U.S. forces in the future, noting that former detainees have been seen back in combat.

About 150 detainees were released before the start of the tribunal process, a couple dozen of whom were determined not to be enemy combatants, England said.

The combatant review system includes the initial combat status review tribunals and annual reviews for those determined to be enemy combatants. Lawyers for some detainees have begun demanding to interview them to make preparations for hearings in federal court in Washington, D.C.

"These are very complex issues," England said at a Pentagon news conference yesterday morning, calling the decisions difficult. "The information, many times it's ambiguous, it's conflicting. It's not always black and white."

Staff writer John Mintz contributed to this report.