WASHINGTON - The hundreds of nuclear missiles that have stood war-ready for decades in underground silos along remote stretches of America, silent and unseen, packed with almost unimaginable destructive power, are a force in distress, if not in decline.

They are still a fearsome superpower symbol, primed to unleash nuclear hell on a moment's notice at any hour of any day, capable of obliterating people and places halfway around the globe if a president so orders.

But the number of intercontinental ballistic missiles, or ICBMs, is dwindling, their future defense role is in doubt, and missteps and leadership lapses documented by The Associated Press this year have raised questions about how the force is managed.

The AP revealed one missile officer's lament of "rot" inside the force, and an independent assessment for the Air Force found signs of "burnout" among missile launch crews.

The AP also disclosed that four ICBM launch officers were disciplined this year for violating security rules by opening the blast door to their underground command post while one crew member was asleep.

After one of the Air Force's three ICBM groups failed a safety and security inspection in August, GOP Rep. Howard "Buck" McKeon of California, chairman of the House Armed Services Committee, said it was time for the Air Force to refocus on its ICBM responsibilities and to "recommit itself from the top down" to safe nuclear operations. Air Force leaders say the nuclear mission already is a priority and that the missiles are safe and secure.

Gen. Mark Welsh, the Air Force's top officer, told the AP in November that since 2008, "the No. 1 focus area, the No. 1 priority for the U.S. Air Force has been to restore and strengthen the nuclear enterprise."

Once called America's "ace in the hole," the ICBM is the card never played. None has ever been fired in anger.

Some say that proves its enduring value as a deterrent to war. To others it suggests the weapon is a relic.

Its potential for mass destruction nonetheless demands that it be handled and maintained with enormous care and strict discipline for as long as U.S. leaders keep it on launch-ready status.

Today it is the topic of a debate engaged by relatively few Americans: What role should ICBMs play in U.S. defense, and at what financial cost, given a security scene dominated by terrorism, cyberthreats and the spread of nuclear technologies to Iran and North Korea?

The Congressional Budget Office on Friday estimated that strategic nuclear forces would cost the Pentagon $132 billion over the next 10 years, based on current plans. That would include $20 billion for the ICBM force alone. It does not include an estimated $56 billion for the 10-year cost of communications and other systems needed to command and control the whole nuclear force.

One prominent American who has questioned the future of ICBMs is Chuck Hagel, the current secretary of defense. As a private citizen in 2012 he endorsed a report that outlined a phased elimination of nuclear weapons, to include scrapping U.S. ICBMs within 10 years. The report by a group called Global Zero said the ICBM "has lost its central utility" in nuclear deterrence.

Since becoming Pentagon chief in February, Hagel has not commented on the future of ICBMs. In remarks last month welcoming a new commander of U.S. Strategic Command, he highlighted the enduring value of nuclear weapons but also cited "troubling lapses" in professionalism within the nuclear force. He was not specific, but aides said he was alluding to a range of recent breakdowns in discipline and training.

One of the most glaring examples of ill-discipline is the case of Maj. Gen. Michael Carey, who was fired in October from his job as commander of the ICBM force. An Air Force investigation of Carey that was released Thursday said that while leading a U.S. delegation on a three-day trip to Russia last summer, he drank heavily, partied with "suspect" local women, insulted his Russian hosts, complained about his bosses and lamented in public settings the low state of morale in the ICBM force.

At the core of the ICBM problem is the reality that the U.S. sees less use for nuclear weapons and aims to one day eliminate them, possibly starting with the missiles. The trend is clear, advanced by President Barack Obama's declared vision of a nuclear weapons-free world.

Last summer Obama directed the military to come up with new non-nuclear strike options, not as a substitute for the weapons but as a key to reducing their role.

Thus the nuclear mission, not just the number of weapons, is narrowing. So apparently is the attraction of being a nuclear warrior.

Pairs of young officers are assigned to ICBM launch centers for 24-hour shifts. They keep a computer-linked eye on the 10 missiles for which they are responsible, waiting for a potential launch order and fighting little but boredom. Some are on their first Air Force assignment. Most were "volunteered" for the duty. Many find it unsatisfying.

John Hamre, a former deputy secretary of defense and now president and chief executive of the Center for Strategic and International Studies, a centrist think tank, says young Air Force officers sense the mission is in decline.

"We are seeing a difficult time sustaining cutting-edge morale at a time when the overall signals coming from the top are that the nuclear deterrence force is no longer a priority," Hamre said. "How do we recruit front-line talent into a field when senior civilian and military leadership never talks about the mission? Young professionals look up for signals. They are seeing the right words, but there isn't energy behind them."

Eugene Habiger, a retired Air Force four-star general who headed Strategic Command from 1996 to 1998, puts it this way:

"It's a real problem to keep those young men and women interested in going on alert three or four times a month for 24 hours at a time when it's hard to explain to them who the enemy is. It doesn't have the allure that it did during the height of the Cold War when you felt like you were doing something."

The current ICBM, known as Minuteman 3, has been in service since 1970. The Air Force operates 450 of them and has suggested cutting to 400 as part of adapting to the new strategic arms treaty with Russia by 2018.

ICBMs are one leg of a strategic "triad" of nuclear weapons delivered by long-range bomber aircraft, submarines hidden at sea and land-based missiles. Together they are said to form the backbone of deterrence, or the ability to convince any potential nuclear attacker that it would lose more than it might gain.

That was accepted orthodoxy during the Cold War, when the fear of nuclear Armageddon was ever-present.

But that day is past.

"The relative importance of the ICBM leg of the triad has diminished in recent years, and its utility for meeting future security challenges is up for debate," Evan Braden Montgomery wrote in assessing the future of America's strategic nuclear force.

His analysis, published Dec. 5 by the Center for Strategic and Budgetary Assessments, questioned the "strategic relevance" of the ICBM force, noting that because the missiles would have to fly over Russia to reach most other potential targets in East Asia and the Middle East, Moscow could mistake such a strike for an American attack on its territory. Montgomery nonetheless concluded that the ICBM force should not be eliminated.

Tom Nichols, an author and professor of national security affairs at the Naval War College, foresees the strategic nuclear arsenal possibly being cut to "low hundreds" of deployed warheads in coming years from its current total of nearly 1,700.

A firm believer in the value of ICBMs, Nichols says that whatever their number as part of a smaller force, the Pentagon should consider taking a portion of the missiles off high alert, meaning those would no longer be ready to launch quickly.

"It would reduce a lot of stress" on those who operate and manage them, he said.