Roche resigned voluntarily and was "not pressured by anyone to resign," said Colonel Jay DeFrank, an air force spokesman.

"He leaves the air force now so that his resignation may free-up nominations of air force general officers that have been on hold in Congress," DeFrank said.

Senator John McCain held up Senate action on nominations for Pentagon posts to pressure the Pentagon to release all e-mail from Roche and other top air force officials related to a 21 billion dollar deal to lease and buy 100 767A tanker planes from Boeing.

Congress finally scrapped the deal altogether in October in passing the 2005 defense authorization bill.

The action came just days after a former top air force acquisition official, Darlene Druyun, was sentenced to nine years in prison for favoring Boeing in a series of negotiations in 2001 and 2002, including the tanker deal.

Druyun, who was later hired by Boeing, admitted among other things to agreeing to a higher price for the Boeing tanker aircraft as a "parting gift" to her future employer, the US Attorney's office said.

Defense Secretary Donald Rumsfeld suspended the the deal pending the outcome of an inspector general's report and an air force review of alternatives for replacing or refurbishing an ageing fleet of KC-135 tankers.

In a statement, the Pentagon said Roche advised Rumsfeld in early October of his plans to step down at the end of President George W. Bush's first administration.

DeFrank said Rumsfeld did not ask for his resignation, and his decision to resign was unrelated to the failure of the tanker deal.

"Secretary Roche remains confident that the merits of the needs to recapitalize our Eisenhower-era tankers stand on their own," he said.

He will leave January 20 or sooner if a successor is confirmed before then, the Pentagon said.

"Jim Roche has led the air force during an important period in history," Rumsfeld said in a statement from Quito, Ecuador, where he was attending a meeting of defense ministers from the region.

Rumsfeld said Roche had served "capably and with honor. I thank him for his service and wish him all the best."

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