WASHINGTON, D.C. - Senator Maria Cantwell says she is blocking Senate action on President Bush's nomination for a new Air Force secretary.

Cantwell, a Washington state Democrat, says she is not convinced that Michael Donley, Bush's choice to lead the Air Force, and other leaders recognize the seriousness of problems with a $35 billion contract for refueling tankers.

In a July 31 letter to Defense Secretary Robert Gates, Cantwell says she's concerned that the Pentagon may not conduct a fair rebidding of the tanker contract, which was initially awarded to Northrop Grumman Corp.

The contract was voided after government investigators found "significant errors" in the Air Force's decision. The Pentagon opened a second round of bidding Wednesday.

Under Senate rules, any senator can block a nomination or legislation by issuing a "hold," or block.