The secretary of the Army is defending his decision to strip awards for heroism from a former Green Beret officer, saying the soldier demonstrated a “lack of honorable conduct” after he earned the medals.

Maj. Mathew L. Golsteyn received the Silver Star in 2011 for valor in Afghanistan on Feb. 20, 2010, and was later approved for an upgrade to the even more prestigious Distinguished Service Cross. That award is considered second only to the Medal of Honor in recognizing heroism in combat.

Golsteyn was later investigated for an undisclosed violation of the military’s rules of engagement in combat — a violation related to the killing of a known enemy bombmaker, according to officials familiar with the case. The investigation closed in 2014 without Golsteyn’s being charged with a crime, but Army Secretary John M. McHugh made the rare decision to strip him of both awards anyway.

The move has been scrutinized by the media and criticized by Rep. Duncan D. Hunter (R-Calif.), a Marine veteran who has advocated on Golsteyn’s behalf. But McHugh stood by his decision in a new letter to Hunter, saying that the senior officer who initially approved Golsteyn’s Silver Star, Gen. David M. Rodriguez, agreed with his decision.

“Every step in the process of investigating Major Golsteyn’s actions, and reviewing and subsequently revoking his valor awards has been thorough, objective and justified,” McHugh wrote in the Feb. 26 letter, obtained by The Washington Post. “The Army’s investigation demonstrated that Major Golsteyn’s service during or at the time of the distinguished act, achievement or meritorious service was not honorable, which led to the revocation of the Distinguished Service Cross.”

A spokesman for Rodriguez referred questions to the Army, saying the issue was a personnel matter. He was the three-star deputy commander of U.S. forces in Afghanistan when he approved the initial valor award for Golsteyn. Rodriguez is now the four-star chief of U.S. Africa Command.

Golsteyn, a former member of the 3rd Special Forces Group and graduate of the U.S. Military Academy at West Point, N.Y., has declined to comment through his lawyer. In recent months, the Army has taken away his Special Forces tab, a qualification that goes to any soldier who completes Special Forces training, and reassigned him to the conventional Army as an infantry officer.

The service also decided recently to separate him from active duty, a move that would likely require Golsteyn to face an administrative board that could issue an other-than-honorable discharge. That could prevent him from receiving medical benefits once out of the military — important because Golsteyn has been diagnosed with spinal damage, a traumatic brain injury and post-traumatic stress, and had an operation on his heart while serving, said his attorney, Phil Stackhouse.

Neither Army officials nor Golsteyn’s advocates have been willing to elaborate on the allegations he faced. The Army began investigating him after he interviewed for a job at the CIA, three sources with knowledge of the probe told The Post in February.

In a letter that month, Hunter told McHugh he was concerned that the investigation and decision to strip Golsteyn of awards were not objective, and he asked for the secretary to confirm that he had nothing to do with quashing an appeal filed by the former Special Forces officer.

After McHugh’s reply on Feb. 26, Hunter fired back with a letter the following day. The congressman wrote that he disagreed with McHugh’s characterization of the investigation, adding that an “allegation relayed by the CIA” could not be used to criminally charge Golsteyn.

“The Army knows this already, of course,” Hunter wrote. “The Administrative actions currently underway are a direct result of the Army’s inability to justify a criminal charge based on the evidence.”

Hunter declined to attend a briefing McHugh offered on the situation if it would only “recite what’s already known, or attempt to justify the political end that the Army has sought to achieve.”