WASHINGTON — The two men nominated to replace the ousted Air Force leadership said Tuesday they'll work to restore trust and confidence in the beleaguered service, under fire for poor handling of its nuclear duties and other missteps.

"I believe the most urgent tasks for the new leaders are to steady this great institution, restore its inner confidence ... and rebuild its external credibility," Michael Donley, the nominee for secretary of the Air Force, told a Senate confirmation hearing.

He said he's met with the service's senior leaders in recent weeks and they are "ready to put the difficulties of the past few months behind them ... to learn the appropriate lessons from these experiences and to move forward."

Donley appeared beside Gen. Norton A. Schwartz, who has been nominated for Air Force chief of staff.

Senators want to hear what Donley and Schwartz will do to take the Air Force in a new direction. But some are skeptical about whether the leadership change can solve systemic problems at the service, especially with only six months left in the Bush administration.

Opening the hearing before the Senate Armed Services Committee, its chairman, Sen. Carl Levin, noted this is a "very very difficult time" for the Air Force.

The Michigan Democrat told the nominees that their jobs "will be to fix the underlying problems and not just the symptoms."

If confirmed, Donley and Schwartz would replace former secretary Michael Wynne and chief of staff Gen. Michael Moseley, fired together in June in an unprecedented decapitation of Air Force leadership that Defense Secretary Robert Gates said was to hold the men accountable for a decadelong decline in the way the service handles the nation's nuclear arsenal.

Gates said his decision was based mainly on the damning conclusions of an internal report on the mistaken shipment to Taiwan of four Air Force fusing devices for ballistic missile nuclear warheads. And he linked the underlying causes of that slip-up to the August incident in which a B-52 bomber was mistakenly armed with six nuclear warheads and flown across the nation without anyone realizing it.

The service also has been widely criticized for problems with its purchasing system. Sen. John Warner, R-Va., noted that over the last four years, congressional auditors have reversed a number of significant Air Force contracts.

In one, the Government Accountability Office last month said the Air Force made "significant errors" in awarding a $35 billion contract for a new fleet of refueling tanker aircraft. The competing companies are making new offers and selection is being overseen by Gates' office, and not the Air Force.

In yet another case, the Pentagon inspector general this year said the 2005 contract to promote the Thunderbirds aerial stunt team was tainted by improper influence and preferential treatment. No criminal conduct was found. Moseley was linked to the scandal, though not blamed directly.

Donley defended the purchasing system, saying in the tanker case, for instance, auditors looked at over 100 items that were questioned and sustained the Air Force on the majority of them.

Donley and Schwartz said in a questionnaire submitted to the committee before the hearing that although the purchase system needs improvement it is "not fatally flawed."