Mysterious circles of light darted and swooped across the Northern Virginia sky last night, prompting dozens of calls to police agencies from curious and concerned citizens.

Observers described the lights as blob-shaped. The lights moved rapidly along a circular track, then hurtled toward the center of the track to merge into a large, bright area.

But they weren't from space. They were from a chain of fast-food restaurants in the area using high-powered searchlights in a promotion.

Beset by what a Fairfax County dispatcher described in mock exasperation as "nine thousand" calls about the sightings, police mounted a rapid investigation. They concluded that the searchlights were being reflected off clouds that hung over the area last night.

"All of us police departments have been getting calls," said a Falls Church police dispatcher. An Arlington dispatcher said some people who called to report the lights were apprehensive, others mainly curious.

Clouds that made possible the apparent reflection covered the sky in much of the area last night. A National Weather Service meteorologist described them as altocumulus clouds, at elevations of 8,500 to 10,000 feet.

Jim Rohls, a regional security manager for the McDonald's restaurant chain, confirmed that some of the chain's outlets were using searchlights. He said they were being used to promote the company's "Kids Combo Meal."

It was not known if all observers saw the same phenomenon last night.