Vast arrays of solar power cells floating in orbit around the Earth could beam back 25 percent of U.S. electricity needs by 2025, according to a scientist who proposed the notion 10 years ago.

The microwave beam of energy would be safe for birds, planes and people and would be a cheap, nonpolluting energy source for the next 5 billion years, Dr. Peter E. Glaser told a press conference. It would cost $10 billion to put the first solar power generator in orbit 20,000 miles up, and it could be done by 1995 with existing technology, he said.

The price includes lands for the field of receiving antennas on earth, six miles across, and the prediction assumes that from three to seen satellites would be built every year until 2025. Each would provide 5 million kilowatts of power, equal to the output of five current nuclear power plants.

Glaser, z consultant for Arthur D. Little Inc., was one of the speakers at the second day of press conferences, seminars, debates and exhibits at the annual convention of the American Association for the Advancement of Science, which is meeting this week at the Sheraton Park Hotel.

"Ten years ago this proposal elicited a plite smile and total disbelief," Glaser said, "but now we are more realistic about our future energy supply situation. The question is not whether it will be adequate but how much time we have lef and how we can best prepare for the shortage."

Studies of the "SunSat" System, as Glaser called it, have been made by the National Aeronautics and Space Administration, the Department of Energy and several academic teams, while Congress had held hearings on the subject. India and Germany are conducting research and Japanese scientists have indicated that manufacturing capacity already exists to supply many of the needed parts, Glaser added.

Ongoing research includes intensive study of environmental and health impact, Glaser continued. He said international agreement should be sought on satellite locations, microwave transmission frequency and management questions, since controversy has already arisen over the claims of some nations on the equator to the space above their land.

Another speaker, Philomena G. Grodzka of the Lockheed Missiles and Space Co., recommended that any international control body by a public corporation like the Tennessee Valley Authority.

Glaser believes that microwave transmission from space would be safe. "I have made a standing offer to provide the wine and salad to anyone who promises to eat the duck that flies through the beam - cooked or not," he said after the press conference.

The safety question and many other aspects of the proposal are highly controversial. Critics have said that lasers (high intensity light beams) would be a more efficient way of transmitting power; the materials to build the satellites could come more economically from the moon or from asteroids: that the investment could be better used on projects on earth to improve the lot of the world's poor.