WASHINGTON — At least 92 Air Force officers assigned to the nation’s nuclear arsenal have been implicated in a proficiency-test cheating scandal and temporarily relieved of their duties, officials said Thursday, announcing that they had temporarily taken out of commission nearly one-fifth of the nuclear force.

The widening scandal, which came to light after a probe into alleged drug use by nuclear operators, has exposed systemic integrity lapses in one of the Pentagon’s most critical, albeit largely unseen, missions.

“This situation remains completely unacceptable,” Air Force Secretary Deborah Lee James said Thursday. “I believe now that we do have systemic problems within the force.”

James, who recently returned from a trip to Air Force bases where she met with airmen assigned to the nuclear mission, said the cheating scandal appears to have emerged within a field beset by “undue stress and fear.”

“I heard repeatedly that the system can be very punitive, come down very hard in the case of even small, minor issues that crop up,” she said, adding that airmen feel they are not duly rewarded or acknowledged for solid performance.

James, who was sworn in last week, said the proficiency tests were being used as the main, if not sole, basis to promote officers. The 92 suspended officers were either caught cheating on the test or found to have turned a blind eye to the lapses, officials said.

“I believe that a very terrible irony in this whole situation is that these missileers didn’t cheat to pass, they cheated because they felt driven to get 100 percent,” she said. “Getting 90 percent or 95 percent was considered a failure in their eyes.”

The 92 officers who were decertified are based at Malmstrom Air Force Base in Montana. Personnel at the base oversee 150 Minuteman III nuclear missiles, one-third of the nation’s Minuteman III arsenal. The base is one of three where America’s 450 intercontinental ballistic missiles are kept.