November was not a good month for Terraset, the fancy new solar-heated school set into a Reston hillside. Its solar energy collectors installed last spring amid much publicity, need direct sunlight to heat the water that heats the school. November offered only two clear days, according to the National Weather Service.

In addition, the solar heating system itself sprang some leaks. Since it opened, in fact, Terraset has mostly been using its backup heating and hot-water system, a conventional electric boiler. Even so, there are so many other energy-saving features in the experimental buildings that it saved $7,600 in heating costs between April and August, school officials said.

There are days when the solar energy we collect does all the heating, and we collect does all the heating, and some days when it doesn't do any," said Anthony marin, the mechanical engineer who manages Fairfax County school energy conservation program. "Recently. "Recently it hasn't done any."

Terraset was built mostly inside a hollowed-out hill under the watchful eyes of a Saudi Arabian university. The University of Petroleum and Minerals in Dhahran and the Saudi government put up $650,000 for its construction on condition they be permitted to learn from it about ways to exploit the sun, the other major energy resource in Saudi Arabia besides oil. Crown Prince Fahd attended the May, 1976, dedication.

"Theoretically when everything is working properly we should only use the backup boiler under extenauting circumstances - an unoccupied building and a very cloudy day and very cool outside temperatures," said Alcon C. Hlavin, director of Fairfax county educational facilities and construction.

It has not worked that way, however. Terraset's problems with the technology and with the weather are examples of the reasons some energy experts give for saying solar power is a long range solution to the energy crisis but cannot yet be taken seriously.

Solar power advocates, on the other hand, say problems like Terraset's persist only because no major effort has been put into solving them. The difficulties facing solar power, they insist, are only technical. They are not actually that difficult considered the massive amounts of money and the health issues involved in exploiting coal, increasing oil recovery and pursing nuclear fusion among various current efforts.

The school, which cost $3.4 million and has 990 pupils, prominently displays its solar collectors on a special iron rack. Pressurized water under computer control flows through the 4,760 collecting units in 4,822 feet of tubes and is kept at a temperature of 180 to 240 degrees Fahrenheit on sunny days. It doesn't boil because it is uder pressure.

On cloudy days, three 10,000-gallon insulated storage tanks hold the hot water, giving its heat up gradually to warm the building and supplying the hot water taps. There also is a $500,000 heat reclamation system that recycles heat from lights and machines and even body heat from the people in the building. "The solar part hasn't been doing what we wanted it to do but we're stillsaving energy," Hlavin said.

The solar units not even go into operation until the last days of August because of what Martin called minor problems and leaks in some of the rubber seals around each of the tubes. "Some of them just weren't tightened down enough," he said. "The workmen might have been sloppy on a particular day or something." Small temperature senors mal-functioned and were replaced, he said.

Martin said he was confident that once all the startup difficulties are solved, the solar system will operate as predicted to cut Terraset's fuel use another 30 per cent.

"In a perfect situation there would be very cold, very sunny weather, but colar can be economic even here," he went on. "There's a net contribution even on cloudy days."

Terraset was never intended to justify itself economically anyway, he said. "If it were, we'd have done it differently. We wouldn't have displayed the collectors so expensively and wouldn't have remote control capability on the computer." He said he takes home aportable computer terminal on weekends to check periodically on the system's operation.

"This is a demonstration experiment. We wanted to get experience in solar technology and have the public become familiar with at least one type of system. This one is very expensive - we estimate 40 years of recover the cost," Martin continued. "But as the price of oil goes up and the cost of technology comes down it'll get more economic. You have to start somewhere after all."