Last Wednesday in Washington, the House of Representatives approved a bill authorizing research to address the supply of rare earths, saying the minerals were critical to energy, military and manufacturing technologies.

Japanese companies generally avoid discussing their mineral holdings. But experts say that some manufacturers have been stockpiling rare earths, building inventories ranging from a few months’ to a year’s worth. Last Friday, Mr. Ohata, the trade minister, said the government was considering starting a stockpile of rare earths as a buffer against trade interruptions.

Heightened interest in alternative sources has also been an impetus to plans to reopen or establish new rare earth mines in a handful of countries around the world, including South Africa, Australia and Canada, along with the United States, where Molycorp intends to expand a mine in Mountain Pass, Calif. The Japanese trading company Sojitz is negotiating the rights to a rare earth mine in Vietnam, while the industrial conglomerate Sumitomo plans to work with Kazakhstan’s government to recover rare earth elements from uranium ore residues.

Japan is also pushing for new manufacturing processes that do not require rare earths. Last week, the government-affiliated New Energy and Industrial Technology Development Organization, or N.E.D.O., announced that it had developed a motor for hybrid vehicles that used cheap and readily available ferrite magnets, instead of the rare earth magnets typically required.

Hitachi Metals, meanwhile, is working on a magnet that minimizes the use of rare earths by employing copper alloys.

“Japanese companies have become painfully aware of the risks of relying so greatly on China for strategic metals,” said Akio Shibata, chief representative at the Marubeni Research Institute in Tokyo.