PALMDALE, Calif.  — A huge wildfire in the high desert wilderness north of Los Angeles jumped an aqueduct on Friday, rushing toward hundreds of houses as firefighters also tried to keep flames from damaging power lines that bring electricity to Southern California.

Some 2,000 structures were threatened and 300 homes were evacuated, Gov. Arnold Schwarzenegger said.

Winds apparently carried embers across the wide concrete channel, with flames rapidly spreading to backyard fences at the edge of Palmdale. Plumes of smoke streamed across the city of 139,000 as a predicted afternoon increase in winds finally arrived.

Helicopters dipped buckets into the aqueduct to make rapid water drops. No homes immediately appeared to have been damaged. Numerous fire engines were in the area. A giant Boeing 747 supertanker arrived over Palmdale to join the battle.

“As you see, we are deploying everything that we’ve got,” Schwarzenegger said at the fire command post.

Sustained winds of 10 mph to 20 mph were reported, said Los Angeles County fire Inspector Matt Levesque.

“We are actively moving resources to defend that area,” he said.

Most of the homes in the area, however, are of recent construction with fire resistant roofs, stucco walls, boxed eaves and landscaped with fire-resistant vegetation, he said. No evacuations were ordered but were recommended.

Temperatures neared 100 degrees with single-digit relative humidity and the National Weather Service predicted gusts in the area up to 50 mph Friday night. The fire has burned more than 20 square miles since erupting Thursday afternoon and was 20 percent contained, Schwarzenegger said.

Elsewhere in the battle, aircraft bombarded flames on ridges above the Antelope Valley on the southern edge of the Mojave Desert, while 750 firefighters working in high heat sought to outflank the blaze no matter which way it moved.

“We want to pinch it off and call it done,” Los Angeles County fire Capt. Andrew Olvera said.

The blaze spread rapidly after breaking out at midafternoon Thursday, triggering overnight evacuations of about 2,000 homes in rural areas and down to the western side of Palmdale.

One house and three mobile home residences were destroyed, another house had roof damage and various other outbuildings and garages were lost in the horse country region, authorities said.

The concrete channel of the California Aqueduct, which runs along the south edge of the Mojave Desert, had helped to contain the blaze.

Southern California Edison said the fire threatened five high-voltage transmission lines, but the California grid operator had put additional generation resources online and customers were not expected to be affected if the utility lost those lines.

Only 21 SCE customers in the fire area were without power.

The Los Angeles Department of Water and Power asked its customers to reduce electrical usage until the threat eased, but added that it had begun local generation and its system was functioning normally.

A DC-10 jumbo jet tanker that can carry 12,000-gallon loads dropped retardant, leaving orange slashes across ridges. Four other air tankers and nine helicopters also attacked the flames.

The fire broke out near a state highway that snakes through the San Gabriel Mountains, connecting Los Angeles to the high desert. Fire investigators were focusing on some workers who were trying to remove a tire rim by hammering on bolts.

Southern California’s big wildfires are usually associated with the fierce Santa Ana winds that blow withering dry air from the interior toward the coast. Winds this week have been blowing inland from out of the southwest as California experiences an unusually cool July with persistent coastal clouds.

Elsewhere, good weather in neighboring Kern County helped firefighters build containment lines around two wildfires that destroyed homes in remote mountain communities earlier in the week.

To the north, a fire that destroyed eight residences and a few outbuildings as it spread across about 26 square miles of the Sequoia National Forest in the Sierra Nevada was 55 percent contained, authorities said.