WASHINGTON — An Air Force unit that operates one-third of the nation’s land-based nuclear missiles has failed a safety and security inspection, marking the second major setback this year for a force charged with the military’s most sensitive mission, the general in charge of the nuclear air force told The Associated Press on Tuesday.

Lt. Gen. James M. Kowalski, commander of Air Force Global Strike Command, said a team of “relatively low ranking” airmen failed one exercise as part of a broader inspection, which began last week and ended Tuesday. He said that for security reasons he could not be specific about the team or the exercise.

“This unit fumbled on this exercise,” Kowalski said by telephone from his headquarters at Barksdale Air Force Base, La., adding that this did not call into question the safety or control of nuclear weapons at Malmstrom Air Force Base in Montana.

“The team did not demonstrate the right procedures,” he said, and was rated a failure.

To elaborate “could reveal a potential vulnerability,” he said.

In a written statement on its website, Kowalski’s command said there had been “tactical-level errors” in the snap exercise, revealing “discrepancies.”

Without more details it is difficult to reliably judge the extent and severity of the problem uncovered at Malmstrom, home of the 341st Missile Wing, which is one of three nuclear missile wings. Each wing operates 150 Minuteman 3 intercontinental ballistic missiles on alert for potential launch against targets around the globe.

A spokesman for Rep. Howard “Buck” McKeon, R-Calif., chairman of the House Armed Services Committee, said that “two troubling inspections in a row at two different missile wings is unacceptable” to McKeon.

A different type of inspection of the 91st Missile Wing at Minot Air Force Base, N.D., in March led the deputy commander of the wing’s operations group to complain of “rot” in the force.