The world's largest power station using solar cells was turned on last week at the Mt. Laguna Air Force Station, 60 miles east of San Digeo.

The $1.6 million power plant, a solar demonstration project sponsored by the federal departments of energy and defense, will convert sunlight directly into electricity, using 97,000 individual solar cells.

The system will produce about 10 percent of the daytime electricity needs of the 141 people who live and work at the remote radar station.

By comparison to large utility-run power plants, the Mt. Laguna system is minuscule, producing 60 kilowatts of power when the sun is shining, compared to the million kilowatts produced by a large nuclear, coal or oil-fired generating plant.

The solar generating station is one of a series of such projects planned by the Department of Energy to demonstrate the practical application of photovoltaic systems, which convert sunshine directly into electricity.

Solar power is already economical when used to heat water for use in households and swimming pools. But the large-scale use of sunshine to produce electricity has become economically feasible only with the development of cheap solar cells.

The Mt. Laguna project will not be the world's largest solar generating station for long, according to Rob Stern, a spokesman for the Department of Energy in San Francisco.

Bigger plants are already in the planning stages, Stern said, and eventually, if costs continue to drop for the now-expensive solar cells, private industries will begin building plants of their own.

The Department of Energy projects in a sense are providing start-up money for an infant solar cell industry, one in which a large volume or production should mean a significant drop in costs.

Stern compares that development to the economies experienced in the production of semiconductors used in computers, calculators and home appliances.

The price of solar cells already has dropped significantly, from about $30 per watt in 1975 to about $8 per watt today.

The price will have to fall even further -- to less than $1 a watt -- before solar cells become practical in a widespread application, Stern said.

The Department of Energy is predicting that will happen by 1986. By then the solar industry will be manufacturing 500 megawatts worth of solar cells, the equivalent at peak output of the San Onofre nuclear power station north of San Diego, which now provides power for nearly 500,000 households.

Photovoltiac systems still cost seven to 15 times as much as nuclear or coal plants for each kilowatt of electricity, according to Richard Pierson of the California Energy Commission's solar office.

But U.S Department of Energy officials are predicting that the cost of solar cell cystems will drop below the cost of other electricity-generating systems by 1990.

There is still a considerable number of uncertainties about a future in which sun-fueled generating plants satisfy a significant percentage of the nation's power needs.

The Mt. Laguna system has no storage capability and operates only as long as the sun shines.

The radar base until now, however, has produced its own power with a diesel generator.

The solar cells will supplement that source of power using an automatic system that will begin feeding in the solar power as the sun rises each day. The system disconnects itself when cloud cover drops the solar power to less than 5 percent of its capacity.

While the station has no storage system for supplying solar power around the clock, the system should save some 11,500 gallons of fuel a year by reducing use of the diesel-powered generator.

In an age of continuous inflation, the solar systems are actually falling in price. The $1.6 million plant could be built today for 40 percent less, according to the U.S. Army's Mobility Equipment Research and Development Command, which helped develop the Mt. Laguna system.

"Given time," the Army said, "such systems might be constructed for less than $100,000."

The largest solar electricity system in operation until now has been a 25-kilowatt generator used for an irrigation project in Mead, Neb., an earlier Department of Energy project.