Representatives of the solar electric power industry, facing a 59 percent cut in federal support by the Reagan administration, disagreed at Senate hearings yesterday on how such a reduction would affect the U.S. position as world leader in photovoltaic energy technology.

Joel Weiss, representing Acurex Solar Corp., warned that the administration's 1982 fiscal-year budget cutbacks could permit competitors in France, West Germany and Japan, backed by growing support from their own goverments, to overtake the United States' 85 percent foreign-market share.

The greatest immediate demand for photovoltaic devices -- energy cells that generate electricity when exposed to the sun -- will be in Third World regions where no central electric service exists, industry officials noted. But those areas are targets for increasing competition by foreign producers, Weiss said.

His concern is shared by two-thirds of the infant, $35 million-a-year U.S. solar industry, said Allen I. Mendelowitz of the General Accounting Office, reporting on a survey of the U.S. industry at hearings before the Senate Energy subcommittee on research and development.

However, William E. Bicker of Arco Solar Industries, a subsidiary of Atlantic Richfield, a major U.S. oil company, sought to minimize the impact of the Reagan budget cuts. "The $62.9 million requested for fiscal 1982 by the administration is more than is needed to achieve the major objectives of the program," he said. The U.S. industry is strong enough to solve the remaining technological hurdles without heavy federal support, he said.

The federal government has so far contributed $600 million to speed the development of solar energy, with much of the backing concentrated in the periods after the 1973 Arab oil embargo and the energy alarms of 1978 and 1980. Support has included research to help U.S. firms lower the costs of solar devices and, to a smaller extent, the purchase of solar devices by the government to stimulate sales.

Bicker said the chief support needed now is a continuation of the current tax credits of up to 25 percent for companies that buy photovoltaic systems.

That view was challenged by John Goldsmith of Solarex Corp., the Rockville firm that ranks with Arco Solar as industry leaders. In an interview preceding his testimony, he said that with continued strong federal support, the industry could reach its historic goal of making solar electric energy prices competitive with electricity from coal and other conventional sources by the end of the decade.

With that bridge crossed, solar energy could become a significant alternative energy source by the end of the century, if oil does become scarce, Goldsmith said.

Without that support, the industry's growth will be much slower, he maintained.

The goals of the old solar program, he said, "have suddenly disappeared, are no longer discussed and have been written off the books."