Cost of F-22 fighter for Japan as much as $250 mln

* Sources describe Sen. Inouye letter to Japan ambassador

* US Air Force said more supportive of possible exports

By Andrea Shalal-Esa

WASHINGTON, June 5 (Reuters) - The U.S. Air Force estimates it would cost Japan as much as $250 million per plane to buy dozens of radar-evading F-22 fighter jets, a U.S. senator told Japan's ambassador in a letter, saying he hopes to reverse a current U.S. ban on such exports.

Senator Daniel Inouye, who heads the Senate Appropriations Committee, said this price included the cost of creating an export version of the most advanced U.S. fighter, built by Lockheed Martin Corp (LMT.N). This assumes production would begin in four to five years, with deliveries in seven to nine years, according to two sources familiar with the letter.

Rob Blumenthal, a spokesman for Inouye, confirmed the senator had sent letters on the F-22 issue to the ambassador, Ichiro Fujisaki, and to Defense Secretary Robert Gates. He declined to release the letters or discuss their content.

The sources, who asked not to be named since the issue is still far from decided, said the U.S. Air Force had reversed its opposition to F-22 exports after studying the issue of F-22 exports again over the past four to six months.

The estimated cost is far higher than the roughly $150 million paid by the Air Force for its last batch of fighters, but the price tag would come down considerably if Congress decides to add funding for more U.S. F-22s to the fiscal 2010 budget, the sources said.

"That would help quite a bit because it would avert the cost of restarting the production line once it had stopped," said one of the sources.