TSURU, Japan — The experimental MLX01 maglev is the world’s fastest train. But it is confined to a 12-mile track. And like the train itself, its technology has been trapped in Japan.

Now, though, Japan wants to begin exporting its expertise in high-speed rail.

On Tuesday, the Central Japan Railway Company took the visiting United States transportation secretary, Ray LaHood, on a test run — a 312-mile-an-hour tryout for the lucrative economic stimulus contracts that the United States plans to award to update and expand its rail network.

“Very fast,” Mr. LaHood said after stepping off the maglev at a track nestled here in mountains west of Tokyo. “We’re right at the start of an opportunity for America to be connected with high-speed, intercity rail,” he said.

The overseas push is a big turnabout for Japan, which long jealously protected its prized bullet train technology. But lately Japan has been forced to rethink that, prompted by a declining market for passenger and freight traffic at home, as well as a flurry of overseas opportunities.