The Air Force is asking for new bids on a $40 billion contract for aerial refueling tankers, and taxpayers can only hope the decision this time isn't hijacked by political considerations.

Last time around, the Air Force awarded the contract in February 2008 to a European supplier whose bid was slightly lower than its American competitor, Boeing. That prompted cries in Congress that the process was unfair and un-American.

Boeing protested, and the Government Accountability Office found that the Air Force failed to evaluate the proposals from Boeing and Northrop Grumman/Airbus on the same merits. The contract was spiked.

The effort to hire a contractor to build new tankers began seven years ago. Meanwhile, the Air Force's fleet of 500 refueling tankers isn't getting any younger. Some of these huge planes that provide fuel for fighter jets in midair are nearly 50 years old, and need to be replaced soon.

As Defense Secretary Robert Gates has said, the bidding process has been bedeviled by "parochial squabbles and corporate food fights." That can't happen this time, and it's the responsibility of the Air Force and Congress to make sure the process is fair and free of politics.

But don't count on it. Already there are signs that powerful pols in Congress are trying to inject themselves into the process.

For example, Rep. John Murtha, D-Pa., chairman of the House Appropriations defense subcommittee, wants the winning contractor to build the planes twice as fast as the Pentagon has requested. But it's not clear where the extra money up front would come from. And there's always the risk that such interference could favor one bidder for reasons that have nothing to do with cost or job performance.

Congress often can't resist meddling in defense contracts, especially when jobs back home are at stake.

The latest defense spending bill in the Senate contains $2.65 billion in pork-barrel "earmarks" inserted by congressmen. It would add $1.7 billion for a destroyer the Defense Department did not want, and $2.5 billion for 10 C-17 cargo planes the Pentagon did not request.

Murtha was among the leaders in earmarks in the House defense bill, with more than $73 million in projects. Many of the favored firms employ people who are generous campaign contributors to Murtha.

Air Force officials say this time they have scrapped the most confusing and contentious portions of the tanker contract, and cut the list of requirements in half. The Pentagon hopes to select the winning bid next summer.

Given the messy history of this bidding process, Gates and his top brass must be more vigilant this time to ensure that the competition is fair, transparent, and free of undue political interference.