George W Bush has declared California a major disaster zone after wildfires prompted the biggest US evacuation in the state's modern history.
Four days of fires have killed three people, injured 40 and burned 1,500 homes, causing some $1bn in damage.
More than 500,000 people have been ordered to evacuate as fierce winds fan fast-moving fires that have ravaged land from Santa Barbara to Mexico.
Forecasters say winds are weakening, easing conditions for firefighters.
In some areas, wind speeds were down to 21-36 mph (34-58km/h), from highs of 100mph earlier in the week.
California Governor Arnold Schwarzenegger praised the "great co-ordination" and "immediate response" of federal, state and local government agencies to the fires.
He also thanked President Bush for signing the disaster declaration, which will free federal funds to help governments, families and individuals recover from the devastation wrought by the blazes - at least 16 of which are still burning.
Earlier on Wednesday, Mr Bush declared a state of emergency in seven California counties. He will visit the state on Thursday.
"I will continue to make sure that our efforts are co-ordinated, and that we are responsive to the needs of people... we offer our prayers and hopes that all will turn out fine in the end," Mr Bush said.
The head of the Federal Emergency Management Administration (Fema), David Paulison, said the government had learnt its lesson after it was accused of a sluggish response to Hurricane Katrina on the Gulf Coast two years ago.
"What we see now that we did not see during Hurricane Katrina is a very good team effort from the local, the state and the federal government and across the federal agencies," Mr Paulison said.
More than 400,000 acres (162,000 hectares) of land have been scorched - an area bigger than New York City - and 25,000 buildings are threatened.
Forestry officials say the seasonal Santa Ana winds are hampering their efforts to contain fires raging across the state, and high wind warnings are in effect for most of the region until Wednesday afternoon.
In San Diego County, which has been hardest hit and where five blazes are still burning, the bill just from damage to homes will top $1bn (£500m), said San Diego County emergency services director Ron Lane.
Firefighters there have been working around the clock in difficult conditions.
"We've been faced with embers from that fire floating in the air a half-a-mile to three-quarters of a mile away from the fire, underneath people's roofs, on to their back yards, starting those things on fire," spokesman Maurice Luque told the BBC.
One San Diego firefighter, Mitch Mendler, said: "It was like Armageddon. It looked like the end of the world."
Mr Schwarzenegger thanked the firefighters for their tireless efforts.
"They are working 24 hours a day around the clock - and when I say 24 hours around the clock I mean the day only has 24 hours - but in fact many of them that I have met actually work 36 hours and 48 hours without stopping," he said.
County officials placed evacuation calls to 346,000 homes, ordering about 560,000 people to leave - although some 50,000 were allowed to return late on Tuesday.
In Orange County, officials said the number of fires had stretched resources to breaking point.
More than 10,000 evacuees stayed overnight at Qualcomm Stadium in San Diego, while other residents sought shelter in schools, community centres and fairgrounds.
"I'm worried for my baby, my house, my kids, everything," Ana Ramirez, a 30-year-old pregnant woman who was taking shelter in the stadium with her four-year-old daughter, told Reuters news agency.
Ambulances and school buses moved hundreds of people from hospitals, nursing homes and prisons.
The blazes are the worst to hit California since 2003 wildfires that killed 22 people.