More than 7,000 firefighters in better-than-expected conditions managed to extend their lines around a huge and unwieldy wildfire that has threatened thousands of homes for well over a week and fouled the air in two states.

The King Fire east of Sacramento was 35 percent contained Tuesday after burning about 140 square miles and destroying a dozen homes, said the California Department of Forestry and Fire Protection.

Expected high winds up to 35 mph that could stoke the flames and send embers flying ahead of the blaze failed to materialize Tuesday but could still come Wednesday.

"We're not sitting back and waiting. We have crews trying to get those containment lines strengthened," said state fire Battalion Chief Scott McLean.

Nearly 2,000 firefighters were brought in as reinforcements Tuesday, bringing the total to about 7,400.

"This is the highest priority fire in the nation," McLean said. "We're hopeful that we can combat it."

The wildfire, which authorities believe was deliberately set on Sept. 13, has destroyed 12 homes and 57 outbuildings. It continues to threaten about 21,000 structures, more than half of them homes.

Evacuated homeowners in the White Meadows area near Pollock Pines about 60 miles east of Sacramento were allowed to return Tuesday, El Dorado Sheriff John D'Agostini said.

About 2,700 people remain under evacuation orders, fire officials said. The fire also threatens a key University of California, Berkeley, research station that is home to scores of experiments on trees, plants and other wildlife.

The National Weather Service issued a "dense smoke advisory" for Reno, Nevada, and around Lake Tahoe, which is about 15 miles from the fire.

The air quality index was rated "hazardous" for the city of Auburn northeast of Sacramento, as well as the Roseville and Rockville areas.

The man charged with starting the fire, Wayne Allen Huntsman, 37, has pleaded not guilty to arson.