ALBUQUERQUE — During his eight years in the Air Force, Staff Sgt. Justin Lahl grew adept at keeping his sexual orientation a secret — wincing inwardly when fellow airmen made homophobic wisecracks, nodding with a smile when others would caricature gay people for laughs.

He was painstakingly careful about whom he trusted, telling only his roommate and a few friends that he was gay.

These days, though, Sergeant Lahl, a 26-year-old aircraft mechanic, is not only open about his identity, but he has also become a leader of the Gay-Straight Alliance here at Kirtland Air Force Base, a support group for gay and lesbian service members that is the first of its kind in the Air Force.

The new organization at Kirtland, founded with the approval of the base’s commander, is one of a handful of similar groups that have been forming at bases around the country since President Obama repealed in 2011 the military’s “don’t ask, don’t tell” policy, which barred openly gay and bisexual people from serving in the military.