WASHINGTON — Two Air Force officers overseeing nuclear-armed missiles at a Montana air base are being investigated for involvement in illegal drugs, the latest in a string of misconduct cases involving officers who look after the nation’s atomic weapons.

The disclosure Thursday of the investigation at Malmstrom Air Force Base was especially embarrassing for the Pentagon because Defense Secretary Chuck Hagel spent the day visiting intercontinental ballistic missile facilities in Wyoming and Nebraska in an effort to lift morale in the beleaguered nuclear force.

Jennifer Cassidy, an Air Force spokeswoman, said two missile launch officers at Malmstrom were suspected of illegal drug possession. She refused to provide details, citing an ongoing investigation by the Air Force Office of Special Investigations.

Another senior Defense Department official said that the two officers were assigned to the 341st Missile Wing, which controls Minuteman 3 missiles. Both have been barred from missile launch duty and their access to classified information has been suspended until the investigation is completed.

Last month, the Air Force released details of its investigation of Maj. Gen Michael Carey, the former commander of the intercontinental ballistic missile force. He was relieved of command in October after it was determined he drank heavily, made rude comments and spent time with “suspect” women while leading a U.S. government delegation to a nuclear security exercise in Russia last summer.

Experts say other security lapses and discipline problems in recent years can be traced, in part, to the once-elite nuclear force’s perceived decline in importance with the end of the Cold War and the U.S. withdrawal from Iraq and Afghanistan.

In remarks Thursday, Hagel acknowledged low morale among some Air Force personnel assigned to missile silos and other nuclear facilities.

“They do feel unappreciated many times. They are stuck out in areas where not a lot of attention is paid. And I know they wonder more than occasionally if anybody’s paying attention,” he told reporters after visiting Kirkland Air Force Base in New Mexico, home of the Defense Nuclear Weapons School.

Hagel said a group of nuclear weapons officers he met in November told him they had doubts about whether they would remain in the Air Force.

“These young, smart people wonder, ‘What am I doing with my life, is it important, does it make a difference?’” he said.

Hagel did not refer directly to the drug case or the other misconduct incidents when he met about 200 airmen at F.E. Warren Air Force Base, headquarters for the organization in charge of ICBMs, in Cheyenne, Wyo.

But he warned them, “In what you do every day, there is no room for error. None.”

He also toured a Minuteman 3 launch control center in Nebraska that controls 10 missiles, each in an underground silo. There are also missile silos in Wyoming, Colorado, Montana and North Dakota. The missile force remains on high alert, with pairs of officers on duty in the launch control centers around the clock.