PARIS (Reuters) - The leaders of France and Germany said they would consult their EU partners over concerns that protectionism is at play in a big U.S. military tanker deal that looks set to go to Boeing.

U.S. defense contractor Northrop Grumman and its European partner EADS withdrew last week from a long-running competition to supply tanker planes to the U.S. Air Force, saying the rules favored rival Boeing.

In a rare joint statement, French President Nicolas Sarkozy and German Chancellor Angela Merkel called on U.S. authorities to "reject protectionist temptations."

"The Chancellor and the President of the Republic, together with the European Commission and the European partners concerned, will examine the implications of future developments in this affair," the statement said.

They added that EU countries bought three times more U.S. military equipment than they managed to sell to the United States and said it was vital to have fair trading terms.

"The Chancellor and the President of the Republic stress that transatlantic economic relations should be based on open markets and fair trade ... including in the defense sector," their statement said.

Boeing is now the sole known bidder for the lucrative contract, which was awarded to Northrop and EADS two years ago in a deal later canceled by the Pentagon.

For EADS, the parent company of the Airbus plane-maker, the withdrawal was a setback in a major push to increase its presence in the U.S. military market.

(Writing by James Mackenzie; editing by Crispian Balmer)