Secretary of Energy Charles Duncan praised a prototype solar energy-powered house he visited here Sunday, but stopped short of commiting the Energy Department to backing a multimillion-dollar expansion of the project.

"This is a great demonstration of what we're going to have to do if we're going to be less dependent on oil, especially foreign oil," he said after completing a short tour of the house put up by Phoenix builder John F. Long.

"When you walk into this house and see the thermometer reading 58 degrees and then go outside in the 104 degree temperature -- and see the electric meter registering the flow of excess electrical power out of the house into the utility grid -- it's really something," Duncan observed.

Long's project utilizes a solar-electric roof with thousands of photovoltaic cells that convert sunlight directly into energy.

The house is unique because it produces energy from the sun's light rather than the sun's heat. Developed with Long's own financial resources, the system has the capability of producing excess energy and selling it back to the utility company.

Duncan said the project is a perfect example of how differing levels of government and the private business sector can work together to solve the nation's energy problems.

He said the existence of the house underscores the Carter administration's commitment to solar energy development, a commitment questioned by some solar enthusiasts.

Duncan added that increased consumer demand and greater economies are needed to bolster solar energy development.

"Solar energy is going to become a major component of [U.S.] energy independence," he predicted.

Long unveiled the house May 23, just a few days after the Energy Department awarded him a $260,000 grant to defray the cost of the photovoltaic roof system, which Long had paid for with his own money.

In several weeks, Long plans to submit a proposal to the department for a grant of $3.5 to $4 million to expand the photovoltaic system into a small community of 116 houses. His dream, he said, is for a desert community of 75,000 houses by the turn of the century. He maintains that he can reduce the cost of electricity produced by such homes from $10 to $2 per kilowatt.

Duncan said that while "there is a large, large part of the country that can use this," DOE staffers must study Long's request before deciding whether to commit federal money for it.