Sgt. Bowe Bergdahl spent four weeks in basic training with the United States Coast Guard in early 2006 before he was given an administrative discharge, military officials said Wednesday. The disclosure raised new questions about whether Sergeant Bergdahl should have been allowed to enlist in the Army two years later, and whether he had to be given a waiver to join either because he had previously washed out of boot camp or because of concerns about his emotional fitness.

A Defense Department official said that the Army knew that Sergeant Bergdahl, at the time of his 2008 enlistment, failed to make it through Coast Guard basic training two years earlier. The official said he did not know whether Sergeant Bergdahl had then been required to obtain a waiver for Army service. He enlisted when the military was desperate for recruits for Iraq and Afghanistan; an estimated one in every five were receiving waivers for previous drug use or because of other conduct, “moral” or medical issues.

Sergeant Bergdahl walked off his base in eastern Afghanistan on June 30, 2009, setting off a wide search throughout Paktika Province. He was captured by the Taliban and held for nearly five years before being handed over late last month to American commandos in Afghanistan in exchange for the release of five Taliban detainees being held in the prison at Guantánamo Bay, Cuba.

Military officials on Wednesday did not provide any specific reason Sergeant Bergdahl — who was a private first class when he was captured and promoted while in captivity — left Coast Guard boot camp eight years ago. His separation was first reported by The Washington Post, which said that friends of the sergeant believed he had been discharged for psychological reasons.