WASHINGTON — A worrisome culture of fear that made launch officers believe they had to get perfect test scores to be promoted fueled a widening cheating scandal within the military’s nuclear missile corps, according to Air Force officials.

Half of the 183 launch officers at Malmstrom Air Force Base in Montana have been implicated in the cheating investigation and suspended, signaling deeper morale and personnel problems in a force critical to America’s nuclear security.

Air Force Secretary Deborah Lee James said the scandal hasn’t affected the safety or reliability of the military’s nuclear mission. Speaking to Pentagon reporters Thursday, James and Lt. Gen. Stephen Wilson, who heads the Global Strike Command, said that so far it appears the cheating was confined to the Montana base, even while a climate of frustration, low morale and other failures permeates the nuclear force, which numbers about 550.

The cheating scandal is the latest in an array of troubles that now have the attention of senior defense officials, including Defense Secretary Chuck Hagel. The Associated Press began reporting on the issue nine months ago and revealed serious security lapses, low morale, burnout and other problems in the nuclear force. The Air Force recently announced the cheating scandal, which grew out of a drug investigation.

“These tests have taken on, in their eyes, such high importance, that they feel that anything less than 100 could well put their entire career in jeopardy” even though they only need a score of 90 to pass, said James, who recently took over as secretary. “They have come to believe that these tests are make-it-or-break-it.”

The launch officers didn’t cheat to pass the test, “they cheated because they felt driven to get 100 percent,” she said.

Of the 92 officers implicated so far, as many as 40 were involved directly in the cheating, Wilson said. Others may have known about it but did not report it.