By Jill Serjeant

LOS ANGELES, Oct 31 (Reuters) - California's weary firefighters were placed on a new fire alert on Wednesday after weather forecasters warned of hot dry winds this weekend similar to those that sparked 22 deadly blazes last week.

With 3,000 people still out of their homes as firefighters struggled to contain the last four stubborn fires in southern California, Gov. Arnold Schwarzenegger ordered personnel and aircraft to deploy to areas facing high fire risk from the forecast Santa Ana winds.

"We're not out of the danger zone yet," Schwarzenegger told reporters on Wednesday. "We still have four fires.. and we're watching the weather very closely.

"This plan helps ensure that resources are strategically placed and standing ready, prepared for whatever the weekend will bring," he said.

Strong winds combined with triple digit temperatures and parched brush after a record drought were largely blamed for triggering or spreading blazes from Santa Barbara to the Mexican border last week that destroyed 2,300 buildings, caused 12 deaths and drove some 500,000 people from their homes.

Police said on Tuesday that a boy playing with matches had confessed to starting accidentally one of the fires, north of Los Angeles, that burned 63 buildings and charred 38,000 acres (15,000 hectares).

Neither the boy's name nor his age were given. Prosecutors must now decide whether to charge the youth, who is thought to be a preteen.

Most of the fires were believed to have been started by power lines blown down onto tinder-dry brush. One fire, in Orange County, was deemed the work of unknown arsonists. A $250,000 reward has been offered for information leading to the arrest and conviction of the perpetrators.

Some 3,000 people were still under mandatory evacuation orders in the 11-day old Orange County arson-set fire, which was threatening about 200 homes on Wednesday.

In San Diego, firefighters were working to contain fully three other fires ahead of the arrival of more Santa Ana winds. Forecasters have said the winds expected for Friday through Monday were not expected to reach the 80 mph-plus (120 kph-plus) gusts of early last week.

Officials said more than 42,000 people had registered their cell phones and e-mail addresses in order to receive emergency notices and evacuation alerts from San Diego County, which was the worst-affected fire area both last week and in 2003 fires.

The alert ordered by Schwarzenegger deploys air tankers, helicopters, strike and dispatch teams and the California National Guard to potential hot spots in eight counties across southern California.

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