It was not an ordinary school dedication yesterday, but then there is very little that is ordinary about Terrasest Elementary in Reston, one of the first solar energy schools in the country.

Addressing Crown Prince Fahd of Saudi Arabia, Alton C. Hlavin, director of the Fairfax school system construction program, said, "I would like to show you the mechanical room, your royal highness."

And so the prince and his entourage stepped into the boiler room of Terraset, trying to dodge puddles of water as they inspected equipment that Hlavin pointed out.

Overhead, a pipe dripped water onto everyone, it seemed, except Fahd. Secret Service agents looked apprehensively toward the ceiling - dripping water pipes was not one of the problems for which they were prepared.

Prince Fahd came to Terraset because Saudi Arabia provided the $650,000 grant that made the school's solar heating and cooling system possible.

Joining the prince was James R. Schlesinger, President Carter's energy adviser. Schlesinger called Terraset a "remarkable demonstration of partnership between Saudi Arabia and the United States."

That partnership was made possible when the U.S. Energy Research and Development Administration several years ago rejected an application by the Fairfax school system for a grant to finance a solar project at Terraset.

Fahd and his party, which included Prince Saud al-Faisal, spent an hour at Terraset inspecting every corner of the school and joining the dedication program in the auditorium, which serves as a cafeteria during school hours.

The princes, wearing brown robes bordered with woven gold, wore serious and attentive expressions during most of their tour. But their faces broke into broad smiles when a group of Terraset students, wearing their school's colorful yellow and red T-shirts, serenaded them with a chorus of "Bless This House."

Prince Saud acknowledged the question that must have been in some people's minds when he asked, "Why . . . would any Saudi do anything that could conceivably compete with oil?"

But even in Saudi Arabia, Saud said, "we are very much aware of the finite nature of many natural resources. Even though we continue to find additional oil deposts in our country, we know that there is an eventual limit to what we can produce. One of the sources of energy that we expect to utilize as our oil production declines, is solar energy."

Saud said that under th terms of the grant, Saudi engineers, consultants and students will have the right to learn from the Terraset operation, "provided, of course (they don't) interfere with the educational process."

After the dedication program, Fahd, Schlesinger, Saud and the rest of the visiting party were ushered into a convoy of black Fleetwood Cadillacs and taken back to Washington.