(Recasts with firefighters making progress on fourth night)

By Adam Tanner

SAN DIEGO, Oct 24 (Reuters) - Wildfires that have charred a huge swath of California and destroyed 1,300 homes burned into the night on Wednesday, but firefighters said a break in the weather had given them a chance to go on the offensive.

As night fell across the state some 15 fires were still blazing largely out of control, mostly in San Diego County. But a drop in temperatures and weaker Santa Ana winds had slowed their march toward threatened communities.

Around 9,000 men and women fought the blazes as towering flames lit up the sky. Thick smoke hung over much of the lower half of the state, raining ash over homes and cars.

"Today I can finally say its a good afternoon," San Diego County Sheriff Bill Kolender said.

The wildfires have already blackened nearly 800 square miles (2,072 sq km), destroyed 1,300 homes, claimed six lives and injured dozens of people, many of them firefighters.

President Bush, who has declared California's fires a "major disaster," triggering extra federal help, was scheduled to tour the fire areas on Thursday.

The Federal Emergency Management Agency had 1,000 people on the ground in San Diego, Sanders said. FEMA and Bush were both criticized for being slow to respond when Hurricane Katrina struck New Orleans and the Gulf Coast region in 2005.

San Diego County, at the southern end of the state, has been hardest hit by the four days of intense fires, suffering losses in excess of $1 billion, and three of the largest fires still burned out of control there.

"It is just like a chess game as to which area is the highest priority. We are the highest priority now," said Jeff Terpstra, a fire chief at the nearly 200,000-acre (80,940- hectare) Witch fire. "Some of this area hasn't burned for 25 to 45 years. It is destined to burn."

REWARD OFFERED IN ORANGE COUNTY FIRE

After the largest evacuation in California's modern history, some residents were allowed to go home.

"We should have almost all of our people back in their homes by this evening," San Diego Mayor Jerry Sanders said, referring to evacuees within city limits.

One of the most desperate fights was in Orange County, south of Los Angeles, where the 20,000-acre (8,094 hectare) Santiago fire threatened homes in a gated community.

Authorities said federal agents from the FBI and Bureau of Alcohol, Tobacco and Firearms joined local authorities in investigating the Santiago fire as an arson.

"Those are crime scenes," said Jim Amormino, spokesman for the Orange County Sheriff's Department, adding that a $70,000 reward has been posted for information leading to the arrest and conviction of those responsible.

A shift in the wind, from hot dry Santa Ana gusts blowing in from the deserts to an onshore flow of cooler, more moist air coming from the Pacific, helped firefighters hold the line of the flames, which began moving away from populated areas.

"It's the first time we've been on the offense in about three days on that fire, Batallion Chief Kris Concepcion said. "For the most part it its moving away from homes, and there are no homes immediately threatened at this point.

Los Angeles County also reported progress, canceling wind warnings for the first time since the weekend. Top wind speeds fell to below 50 mph (80 kph) after gale force gusts hit 80 mph (130 kph).

San Diego County officials said that even when the fires were extinguished they would face a major cleanup and huge costs. Based on initial estimates, just the homes damaged will be over $1 billion," Ron Lane, San Diego County emergency services director, said. (Additional reporting by Dan Whitcomb in Los Angeles and Dana Ford in San Diego)

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