WASHINGTON – In an extraordinary move, the Army sacked a four-star general who was the subject of a Defense Department investigation into alleged sexual misconduct, officials said Tuesday.

Gen. Kevin P. Byrnes, commander of Army Training and Doctrine Command, was approaching retirement when the decision to relieve him of duty was made by the Army chief of staff, Gen. Peter Schoomaker.

The Army announced no specific allegation against Byrnes, but a senior official said it involved unspecified sexual misconduct. The official spoke only on condition of anonymity because of the sensitivity of the allegation.

Disciplinary action against officers is not rare, but it is extremely unusual in the case of a four-star Army general. An Army spokeswoman, Lt. Col. Pamela Hart, said records from the General Officer Management Office show no cases in recent history in which a four-star has been relieved of duty for disciplinary reasons.

Byrnes, 55, a Vietnam veteran who entered the Army in 1969 as a second lieutenant, ranked third in seniority among the Army’s 11 four-star generals.

A two-sentence statement issued by Army headquarters in the Pentagon said Byrnes had been relieved of his position. It gave no reason except to say, “The investigation upon which this relief is based is undergoing further review to determine the appropriate final disposition of this matter.”

A spokesman at Training and Doctrine Command, Harvey Perritt, said Byrnes was unavailable to comment.

In his position as commander of Training and Doctrine Command, Byrnes oversaw all Army training programs and the development of war-fighting guidelines. The organization operates 33 training schools and centers on 16 Army installations and is headquartered at Fort Monroe, Va. Byrnes had been commander since November 2002.

Among the command’s responsibilities is to oversee Army recruiting and initial recruit training, as well as operation of the Combined Arms Center at Fort Leavenworth, which is responsible for leadership development and the writing of warfighting doctrine. Coincidentally, the commander of the Combined Arms Center, Lt. Gen. William Wallace, was nominated in April to succeed Byrnes at Training and Doctrine Command.

Wallace has not yet been confirmed by the Senate for promotion to four-star rank, so the Army picked Byrnes’ top deputy, Lt. Gen. Anthony R. Jones, to take over immediately as the acting commander.

Asked about the case at a Pentagon news conference, Defense Secretary Donald H. Rumsfeld had little to say.

“It’s something that’s being handled in the proper channels, and it’s not something that it would be appropriate for me to get involved with,” he said.

Other officials said the matter was investigated by the Defense Department Inspector General and the findings were now being considered by senior Army officials to determine whether further action should be taken.

Among the four-star general or flag officers to have been relieved of command in recent years was Navy Adm. Richard C. Macke, sacked as commander of Pacific Command in 1995 for remarks he made about the case of U.S. Marines accused of raping a 12-year-old Japanese girl, and Gen. Michael Dugan, who was fired as chief of staff of the Air Force in 1990 for comments to reporters about planning for the 1991 Gulf War.