The United States agreed Friday on a plan to return 40 percent of the airspace over a U.S. Air Force base in Tokyo to Japanese control, officials said.

The return of the airspace to Japan could shorten flight times to civilian airports, save fuel, and ease congested air traffic in the metropolitan area.

Under the agreement, the United States will return 40 percent of the U.S.-controlled airspace over Yokota Air Base stretching toward Tokyo's Haneda Airport to Japan in time for Haneda's planned expansion in 2009, said a Japanese Defense Agency spokeswoman, speaking on condition of anonymity because of agency policy.

Officials from both countries had been discussing the final details of the deal as part of a broad U.S. military realignment plan.

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The measure would cut flying time for flights to and from Haneda, as well as fuel and other operating costs, the Foreign Ministry said. For instance, flights connecting Tokyo and southern Japan could save about 3 minutes.

"We'll be able to get to the destination faster, and we don't have to waste fuel," Keisuke Okada, an official at the Scheduled Airlines Association of Japan, told public broadcaster NHK.

U.S. military officials in Japan were not immediately available for comment.

About 400 flights a day to and from Tokyo's two main airports of Narita and Haneda are forced to take less-efficient routes when approaching from the west to avoid passing through the U.S.-controlled airspace, which includes parts of Tokyo and surrounding areas, according to airline officials.

American troops have been stationed in Japan since the end of World War II. The U.S. keeps about 50,000 troops in Japan under a mutual security pact.