The Air Force leaders were linked to other controversies. Even before Thursday's revelation of the damning report on nuclear weapons, Moseley's job was thought to be in jeopardy. He had been under investigation by the Pentagon's inspector general for his involvement in the awarding of a $50 million contract to promote the elite Thunderbirds unit based at Nellis Air Force Base.

Investigators showed that senior officers in 2005 pushed the contract to a company, Strategic Message Solutions, whose owners had close relationships with Moseley and other officials, even though the firm's bid was twice as costly as a competitor's.

Gates said his decision to demand the resignations of Moseley and Wynne was "based entirely" on missteps in the Air Force nuclear program.

But the handling of the Thunderbirds contract was among signs that things were amiss in the leadership of the service, according to retired officers and officials in Congress.

Sen. Claire McCaskill, D-Mo., said she believed there was a connection.

McCaskill, a member of the Senate Armed Services Committee, had urged the Pentagon to broaden its investigation of the contract to include the actions of senior officers.

An initial probe that was made public earlier this year assigned blame to Maj. Gen. Stephen Goldfein and two Air Force colonels who received career-ending reprimands.

Goldfein, at the time of the contract discussions, was commander of the Air Warfare Center at Nellis Air Force Base.

Strategic Message Solutions, known as SMS, proposed a so-called "Thundervision" plan to entertain air show spectators with Jumbotron video boards during lulls while the Thunderbirds circled before performing stunts. The $50 million, five-year public relations contract was canceled in 2006. Nellis officials said the "Thundervision" plan was never implemented.

Moseley also has connections to Nellis. He was commander and instructor pilot for the F-15 division at the base in the late 1980s, and was commander of the 57th Wing from 1996 to 1997.

The nuclear-trigger investigation, led by Adm. Kirkland H. Donald, the military's senior official on nuclear safety matters, found that the Air Force was failing to focus on its nuclear mission even after a high-profile incident in 2007 in which a B-52 bomber crew unknowingly flew six nuclear warheads from North Dakota to Louisiana.

Gates was particularly disappointed that the Air Force had not taken significant steps to shore up its nuclear controls after the B-52 incident, said Pentagon press secretary Geoff Morrell.

The nuclear weapons, on cruise missiles attached to the plane's wings, were not discovered missing from their repository at Minot Air Force Base for about 36 hours.

Gates said the dismissals were necessary because the Air Force began focusing on its nuclear problems only after the shipment to Taiwan was disclosed earlier in 2008.

In addition, he said, the Air Force had not been sufficiently critical of its past performance.

Gates acknowledged that problems in securing the nuclear arsenal go back decades, but added that the current leadership should have recognized and corrected them. He appointed a task force led by James R. Schlesinger, defense secretary under President Ford, to recommend improvements in the oversight of nuclear weapons.

Gates said the dismissals of Wynne and Moseley were based solely on Donald's report, which he received last week. The report is classified, but officials briefed on the findings said it was highly critical of Air Force handling of nuclear technology.

The parts shipped to Taiwan included four electrical fuses used to trigger a nuclear weapon aboard U.S. missiles. The fuses were shipped to Taiwan by the Defense Logistics Agency, but the Air Force provided the fuses.

The fuses were sent to Taiwan in 2006. The mistake went undetected until March 2008.

A senior defense official, who requested anonymity because he was not authorized to discuss personnel moves, said the Air Force's failures in nuclear oversight were sufficient to merit the dismissals.

Gates has been critical of Air Force officials' calls to build more F-22 fighter jets, an advanced but expensive plane. He also has been frustrated with the deployment of unmanned aerial vehicles in Iraq and Afghanistan.

Officers have watched with frustration as Gates has delivered a series of speeches seen as critical of the Air Force. In their view, the service has made valuable contributions to the wars in Iraq and Afghanistan, including technology that allows ground troops to see full-motion video shot from Predator drones.

Air Force Lt. Col. Greg Harbin, who has worked closely with Moseley and Wynne, said the two men were very much focused on Iraq and Afghanistan.

"We have not done a good job telling our story," Harbin said. "But there should be no doubt these men were focused on the wars."

The senior defense official said Gates has replacements for the two men in mind.

Air Force leaders are said to favor Gen. John Corley, the head of Air Combat Command, as Moseley's replacement. Other defense officials are supporting Gen. Norton A. Schwartz, the head of Transportation Command.

Stephens Washington Bureau Chief Steve Tetreault contributed to this report.