An Air Force crew damaged a component of an unarmed intercontinental ballistic missile while performing maintenance near a North Dakota base last month, prompting a partial evacuation, military officials said Monday.

Air Force officials said no one was hurt in the Nov. 17 incident near Minot Air Force Base, but it was immediately reported to the highest levels of the Pentagon. A military official, speaking on the condition of anonymity to discuss internal deliberations, said it triggered a “robust discussion” over whether to inform the public.

Ultimately, Air Force officials said they decided to withhold information about the maintenance lapse because they said it did not pose a risk to public safety and because they wanted to avoid needless alarm over nuclear weapons safeguards.

Air Force officials confirmed the incident Monday in response to queries from The Washington Post. Lt. Col. Ron Watrous, a spokesman for the Air Force’s Global Strike Command, said technicians were conducting “routine maintenance” on a section of a Minuteman III missile when a “small replaceable component” was damaged.

He said the component, which he would not describe for security reasons, was not attached to the missile. He said the missile was not armed with a warhead at the time and that no nuclear materials were involved.

The Minuteman III missile has long been a backbone of the nation’s strategic deterrent, or nuclear, forces. The Air Force maintains about 450 Minuteman IIIs at three bases in North Dakota, Wyoming and Montana.

Last month’s incident comes four years after the Air Force committed a series of blunders in maintaining its nuclear arsenal.

In August 2007, a B-52 bomber with the call sign “Doom 99” flew from Minot to Barksdale Air Force Base in Louisiana with the crew unaware that six cruise missiles on board were loaded with nuclear warheads, each with the explosive power of 10 Hiroshima bombs. After landing, the plane was left unguarded for several more hours before the nuclear weapons were discovered.

In March 2008, the Pentagon revealed that the Air Force 18 months earlier had mistakenly delivered nuclear fuses for Minuteman III missiles to Taiwan instead of an order of helicopter parts. The foul-ups bred concern about the adequacy of the nation’s nuclear safeguards, prompted then-Defense Secretary Robert M. Gates to fire the Air Force’s civilian and military leaders, and resulted in a reorganized command structure to oversee nuclear missiles and bombers.

Military officials characterized last month’s damage of a missile component as a serious lapse but not nearly as much of a concern as the earlier incidents.

“On a scale of 1 to 10, this is probably around the 1 to 2 level of seriousness, which is why we didn’t make any statements about this proactively,” Watrous said. “It just doesn’t rise to the level of needlessly frightening the public.”

Military officials said the incident was immediately reported up the chain of command, reaching Air Force Secretary Michael B. Donley and Gen. Norton A. Schwartz, the Air Force chief of staff.

A Pentagon official said Air Force and Defense Department officials came to a “mutual agreement” that a public statement was not needed because it could stoke unnecessary fear.

Brig. Gen. Les Kodlick, the Air Force’s chief of public affairs, called the decision not to publicize the incident “common sense” and “the right answer” because the damaged component did not present a safety risk. “There was never any undue cause for public alarm,” he said.

A military official familiar with the incident, who spoke on the condition of anonymity, said the maintenance crew at Minot dropped the missile component while handling it and that it was damaged after falling about three feet to the ground.

Watrous, the Global Strike Command spokesman, said the Air Force was conducting a review of the incident but still hadn’t determined how the component was damaged. He confirmed that emergency crews had responded but described this as standard procedure.

Some Air Force leaders have recently expressed concern about a lack of experienced officers overseeing the servicing of nuclear missiles.

Maj. Gen. Donald Alston, the commander of the 20th Air Force, said the service has encouraged rising young officers to enter fields related to satellites or space technology instead of nuclear weapons, which some see as a relic of the Cold War. He said this had particularly affected experience levels of maintenance crews caring for intercontinental ballistic missiles, or ICBMs, during what he described as “17 or 18 years of benign and active neglect.”

“I think one thing we absolutely did not do during that time was worry about optimizing the experience levels,” Alston told the trade publication Inside the Air Force in a Nov. 8 interview.

“Where I have a problem is in middle management and senior management, where I’ve got career fields that were diluted. ICBM maintenance is one of them,” Alston added.

Asked whether poor training or inexperience could have played a role in the Nov. 18 incident at Minot, Watrous said the review was continuing. “It would not be responsible at this time to speculate whether experience was a factor,” he said.