The cheating came to light during an inquiry into illegal drug possession, when investigators discovered that test answers were being sent in text messages to the missile launch officers’ cellphones.

The cheating is only the latest in a series of scandals for the Air Force, but is particularly alarming. “You know what the bumper sticker says, ‘one nuclear weapon can ruin your whole day,’ ” said Loren B. Thompson, a military expert and the chief executive of the Lexington Institute, a research group.

Malmstrom, near Great Falls, is one of three bases that oversee the country’s arsenal of 450 intercontinental ballistic missiles. Air Force officials say they have retested about 500 launch officers at the three bases, and that all but 22 of them passed, with an average score of 95 percent. Lt. Gen. Stephen W. Wilson, commander of the Air Force Global Strike Command, said that Defense Department officials do not believe the cheating at Malmstrom extends to the country’s other nuclear launch sites because the tests at each base are different.

But both current and former missileers, as the launch officers are known, say that cheating has been a fact of life for decades. Ms. James said that during her visits to all three bases last week, crew members — while not admitting to cheating — told her that they felt pressure to score 100 percent on the proficiency tests. While 90 percent is considered a passing score, they said that their commanding officers would not promote them unless they scored 100 percent.

“I heard repeatedly from teammates that the need for perfection has created a climate of undue stress and fear,” Ms. James said. “Fear about the future. Fear about promotions. Fear about what will happen to them in their careers.