Lockheed Corp. is developing a solar-powered unmanned airplane that could fly at high altitudes for a year without landing, company officials said yesterday.

The drone, remotely controlled from the ground, would fly about 12 miles high, probably circling over one spot on Earth. Solar cells would provide just enough power for the giant propeller to maintain the plane's position against prevailing winds.

David W. Hall, an engineer with Lockheed Missiles and Space Co. in Sunnyvale, Calif., said NASA and the Department of Agriculture are interested in the plane, which could carry various kinds of sensors and transmit data back as a space satellite does. The plane could be used to monitor crop conditions, he said, and might also have military applications.

"We might put a platform over Central America, and we could monitor communications," Hall said.

Lockheed built two prototype solar-powered planes several years ago that proved the concept, Hall said. Both crashed after about 26 test flights because of structural problems, he said.

Lockheed is now building a plane that will use photovoltaic cells similar to those on the space shuttle for energy. A fuel cell would store power during the day for use at night.

Hall said the plane "looks like it's out of the '20s," with very wide wings. It will use some 1920s materials, such as birch and spruce plywood, and some advanced-technology materials, all intended to keep down weight. The propeller is 40 feet in diameter, he said, "more windmill technology, in reality, than it is airplane technology."

Lockheed believes that the plane could be useful as a low-cost alternative to satellites stationed in geosynchronous orbit 22,300 miles high over single specified spots on Earth.

Since the earlier tests, Lockheed has improved the plane's structure, lengthening the wings and making the craft lighter yet stronger, Hall said. He did not estimate the final cost but said Lockheed has spent less than $1 million on the program so far.

Hall said that a "limited-duration" solar-powered plane could fly soon but that a plane able to fly for longer than a year "at any combination of altitude and latitude" is more than a decade away. The first model would have a maximum speed of about 90 miles an hour.