Hillary Clinton and Barack Obama, the contenders for the Democrats' US presidential nomination, have criticised a Pentagon decision to award a $40 billion (£20 billion) defence order to a European company rather than to the American group Boeing.

Amid fervent campaigning for yesterday's crucial primaries in Texas and Ohio, the Democrat rivals sought to gain political mileage from the Pentagon's decision to buy air-refuelling tankers from EADS, which owns Airbus.

Their opposition to the deal marks the start of intense political lobbying in the US to overturn the contract and raises the possibility that Airbus could lose out if a Democrat is elected president.

John McCain, the Republican Party's likely nominee for president, said that he would wait to pass judgment on the deal until he had been briefed by the Department of Defence.

The tanker contract is the second-largest defence procurement project on record and will be worth an initial $40 billion for 179 aircraft, rising to more than $100 billion in future years. The UK is expected to pick up at least $6 billion of work because wings for all Airbus aircraft are built in North Wales.

EADS was awarded the contract on Friday in a victory that amazed the defence community. Boeing was seen as certain to win, given its position in the US as a corporate giant capable of wielding enormous political influence.

Mr Obama, a US senator for Illinois, Boeing's home state, said that it was hard to believe that “an American company that has been a traditional source of aeronautic excellence would not have done this job”.

Mrs Clinton said that she was “deeply concerned about the Bush Administration's decision to outsource the production of refuelling tankers for the American military”. In a reference to Airbus, she said that it was “troubling that the Bush Administration would award the second- largest Pentagon contract in our nation's history to a team that includes a European firm that our government is simultaneously suing at the [World Trade Organisation] for receiving illegal subsidies”.

The EU is suing Boeing through the WTO alleging the same thing.

Nancy Pelosi, the Speaker of the House of Representatives and a congresswoman from California, where Boeing has factories, said that there could be security implications from using a foreign company to supply tanker aircraft.

Loren Thompson, analyst at the Lexington Institute in Washington, said that although Democrats were kicking up a fuss about the EADS deal now, they might have to soften the rhetoric before the November general election.

He said: “The second-biggest component of this order will be for General Electric engines to power the aircraft. Those are made in Ohio, and Ohio is the most crucial swing state in the general election. I do not think you can win the election without Ohio.”

Boeing's plane would have used Pratt & Whitney engines from Connecticut, which is already a Democratic state and likely to remain so.

Boeing has the option to challenge the decision of the Department of Defence (DoD) and the company yesterday said it would seek an immediate debriefing from the Pentagon - surprisingly aggressive language for a conservative company. Boeing can make a challenge only if it believes that bidding rules have been broken.

Defence analysts said that this would be hard to prove because the DoD has spent more than two years considering which company to select. However, politicians sympathetic to Boeing could try to block the deal in Congress.

This would require some clever arguments as the DoD has clearly stated that the A330 offered by EADS is a more capable plane than Boeing's 767.

Politicians will not want to be seen to be blocking a deal that the Pentagon says is the best for the armed forces. Mr McCain scuppered an early attempt to give the contract to Boeing.

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