WASHINGTON – In a rare move, the Army relieved a four-star general of his command amid allegations that he had an extramarital affair with a civilian, Army officials said Tuesday.

General Kevin Byrnes, 55, led the Army’s Training and Doctrine Command at Fort Monroe, Va., where he supervised the recruitment and academic programs at 33 Army schools, from basic training to the war colleges. General Byrnes, who several military sources said had a previously unblemished record, was set to retire in November after 36 years of service.

The Army released few details about the decision to relieve one of its 11 four-star generals, with spokesmen saying only that General Peter Schoomaker, the Army’s chief of staff, relieved General Byrnes of his command on Monday as the result of an investigation by the Defense Department’s inspector general. A spokesman said Army officials could find no case of another four-star general being relieved of duty in modern times.

Several defense sources familiar with the case, speaking anonymously because the investigation is not complete, said General Byrnes is accused of having an “inappropriate relationship,” and some described him as being involved in an extramarital affair.

General Byrnes, reached by telephone at his home yesterday, declined to comment. His defense attorney, Lieutenant Colonel David Robertson, said the allegation against General Byrnes involves an affair with a private citizen. General Byrnes has been separated from his wife since May 2004; their divorce was finalized on Monday, coincidentally the same day he was relieved of command, Colonel Robertson said.

“The allegation against him does not involve a relationship with anyone within the military or even the federal government,” Colonel Robertson said, emphasizing that the allegations do not involve more than one relationship. “It does not involve anyone on active duty or a civilian in the Department of Defense.”

Having an extramarital affair can be deemed adultery and a violation of the Uniform Code of Military Justice. But such cases rarely go to court-martial and usually end in administrative punishment such as a letter of reprimand, according to military lawyers. Relieving a general of his command amid such allegations is extremely unusual, especially given that he was about to retire.

The Army has been hurt over the past year by detainee-abuse cases and has been accused of not going after top officers allegedly involved in such abuse. Army officials said relieving General Byrnes was meant to show the public that the service takes issues of integrity seriously.

“We all swear to serve by the highest ideals, and no matter what rank, when you violate them, you are dealt with appropriately,” said one Army officer familiar with the case. “Relief of command is a huge consequence. He’s had an extraordinary career, but at the end of the day, the Army has to hold people accountable for their conduct.”

The disciplinary action struck some military experts as severe, given General Byrnes’s reputation as a popular general who has been ushering in systemic changes in Army doctrine and training. A Vietnam veteran who served as the commanding general of the First Cavalry Division and commanded multinational troops in Bosnia, General Byrnes served as director of the Army staff just before taking over at Fort Monroe in 2002.

General Byrnes’s case comes after two prominent Air Force generals were accused publicly of sexually harassing subordinates, and as the Defense Department is revamping its sexual harassment policies.

“It must have been the sort of thing where they felt they had no choice, given the recent history of personnel scandals in the Army,” Michael O’Hanlon, a defense expert at the Brookings Institution, said. “They’re trying to make it clear that four-stars don’t get special treatment. They must feel they have a need to send that message.”

A military defense lawyer in Alexandria, Neal Puckett, said it may be unprecedented to have a four-star general relieved of command for allegations of an affair. He said removing General Byrnes from his office is likely to be the end of his punishment.

“Usually there is no incentive to bring criminal charges, Mr. Puckett said. “There’s not much more that you can do to a high-ranking officer like that. His legacy is ruined.”

Lieutenant General William Wallace was announced as General Byrnes’s replacement in April and has been awaiting Senate review and confirmation. Paul Boyce, an Army spokesman, said Lieutenant General Anthony Jones, General Byrnes’s deputy commander, will take command temporarily while General Wallace’s confirmation is considered.