Foreign nations are "seriously concerned" about a new U.S. satellite policy that could be a "threat to all but the richest and most powerful," the director of the Office of Technology Assessment told a House Government Operations subcommittee yesterday.

The Reagan administration has decided that private satellite companies may keep secret some satellite data they collect and sell it under exclusive contract to one country or company. The decision affects a 25-year-old government policy under which satellite pictures of the earth--including some that show oil and mineral deposit information--have been freely available to all nations or private individuals.

This "open skies" policy has been the foundation of the American space and satellite programs, said John H. Gibbons, director of the Office of Technology Assessment, which is an arm of Congress.

For more than two decades, some countries have complained that land-viewing U.S. satellites in earth orbit were spying on them.

The United States has countered that argument by offering all land satellite images, inexpensively, to anyone or any country that wants them.

The new U.S. policy was created to give a commercial advantage to private companies under the Reagan administration's plan to turn over the nation's land and weather satellites to private companies.