ALPINE, Calif. (AP) _ An arson fire that started in an abandoned Air Force radar building burned more than 3,000 acres of brush in steep terrain, officials said Sunday.

More than 410 firefighters, aided by water-dropping helicopters, had about 70 percent of the blaze on Mount Laguna contained, said Martie Perkins, a spokeswoman for a joint fire command set up by the California Department of Forestry and the U.S. Forest Service.

``Fortunately, the weather is cooperating,'' Perkins said, noting temperatures in the 80s and weak winds.

No injuries were reported and no homes were threatened, but 100 campers and residents were evacuated after the fire broke out at 12:29 a.m. Saturday in the Cleveland National Forest in eastern San Diego County.

The blaze was believed to have been intentionally set, Perkins said.