Fresh from a sobering tour of Japan's leading research facilities, an American scientist told a House committee yesterday that Japan's corporate giants are "racing" toward commercial development of high-temperature superconductors.

"Every major Japanese university and more than 100 corporations are working on these new materials," said H. Kent Bowen, professor of engineering at the Massachusetts Institute of Technology. "We are talking, and they are in high gear."

Bowen was among those who testified yesterday before the House Committee on Science, Space and Technology at its first hearing on new superconductor technology. Superconductors carry electricity without losing energy to resistance, and over the past six months an entirely new class of the superconducting materials has been developed.

As the race to bring them to market has intensified, American scientists, politicians and industrial experts have grown more vocal in calling for a national effort to counter Japan's. So far, many of the basic discoveries have come from American labs, but there is fear that Japan will be much quicker in crafting the materials into useful devices such as wires and computer chips.

Scientists, academics and government representatives convened yesterday to report on progress and puzzle out a national strategy for translating scientific discoveries into economic success.

"The United States of America can continue to talk about unfair policies," Sen. Pete V. Domenici (R-N.M.) testified. "But the truth is, the competition that is defeating us is not unfair. It is just superior."

Domenici called for dedicating at least one of the nine national laboratories to commercial development of the new superconductors. Virtually every national lab is already engaged in superconductor research, but many scientists say that efforts have been duplicated and time wasted.

One of Japan's top researchers, Shinroku Saito, president of the Technological University of Nagaoka, testified that although "superconductivity fever had prevailed all over the world," Japan's Ministry of Trade and Industry had not made an overwhelming effort to consolidate the country's research.

Because superconductors transport electricity without the wasteful resistance of normal conductors, they have vast potential for energy savings as well as electronic uses.

Present superconductors must be cooled by expensive liquid helium, making them expensive to use and impractical for wide applications. But a blizzard of research advances has eased the temperature requirement, and many scientists now foresee room-temperature superconductors that will transform all aspects of electricity.

Researchers captivated committee members with an impromptu demonstration of the new materials' ability to float on a magnetic cushion when drenched with liquid nitrogen.

The research advances have come almost daily, and yesterday one of the witnesses announced a new one.

William R. Graham, science adviser to the president, announced that material scientists at MIT had made a high-temperature superconductor of a metal oxide. The other new superconductors have been ceramics, which are brittle and difficult to fabricate into wires.

Graham said President Reagan was firmly behind efforts to encourage rapid development of the new materials and that the White House had invited 2,500 people to a two-day conference on superconductors in July.

But Graham was challenged by panel members who said the administration had given mixed signals about developing technologies.

"I'm a mother, Dr. Graham, and my children pay a whole lot more attention to what I do than what I say," said Rep. Marilyn Lloyd (D-Tenn.). "You are always full of good intentions, but we are not implementing policy, we are not transferring technology from our labs."

Several people said, however, that there could be no quick answer to America's competitive deficit.

"We need to train people to process materials we develop," said Robert A. Laudise, of AT&T Bell Labs, a leader in working on the new materials. "But this is not something we can do overnight."