Washington ? Defense Secretary Robert Gates ousted the Air Force’s top military and civilian leaders Thursday, holding them to account in a historic Pentagon shake-up after embarrassing nuclear mix-ups.

Gates announced at a news conference that he had accepted the resignations of Air Force Chief of Staff Gen. Michael Moseley and Air Force Secretary Michael Wynne – a highly unusual double firing.

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 electrical fuses for ballistic missile warheads. And he linked the underlying causes of that slip-up to another startling incident: the flight last August of a B-52 bomber that was mistakenly armed with six nuclear-tipped cruise missiles.

The report drew the stunning conclusion that the Air Force’s nuclear standards have been in a long decline, a “problem that has been identified but not effectively addressed for over a decade.”

Gates said an internal investigation found a common theme in the B-52 and Taiwan incidents: “a decline in the Air Force’s nuclear mission focus and performance” and a failure by Air Force leaders to respond effectively.

In a reflection of his concern about the state of nuclear security, Gates said he had asked a former defense secretary, James Schlesinger, to lead a task force that will recommend ways to ensure that the highest levels of accountability and control are maintained in Air Force handling of nuclear weapons.

In somber tones, Gates told reporters his decision to remove Wynne and Moseley was based on the findings of an investigation of the Taiwan debacle by Adm. Kirkland Donald. The admiral found a “lack of a critical self-assessment culture” in the Air Force nuclear program, making it unlikely that weaknesses in the way critical materials such as nuclear weapons are handled could be corrected, Gates said.

Gates said Donald concluded that many of the problems that led to the B-52 and the Taiwan sale incidents “have been known or should have been known.”

The Donald report is classified; Gates provided an oral summary.

“The Taiwan incident clearly was the trigger,” Gates said when asked whether Moseley and Wynne would have retained their positions in the absence of the mistaken shipment of fuses. He also said that Donald found a “lack of effective Air Force leadership oversight” of its nuclear mission.

The investigation found a declining trend in Air Force nuclear expertise – not the first time that has been raised as a problem, Gates said – and a drifting of the Air Force’s focus away from its nuclear mission, which includes stewardship of the land-based missile component of the nation’s nuclear arsenal, as well as missiles and bombs assigned for nuclear missions aboard B-52 and B-2 long-range bombers.

Gates also announced that “a substantial number” of Air Force general officers and colonels were identified in the Donald report as potentially subject to disciplinary measures that range from removal from command to letters of reprimand. He said he would direct the yet-to-be-named successors to Wynne and Moseley to evaluate those identified culprits and decide what disciplinary actions are warranted – “or whether they can be part of the solution” to the problems found by Donald.