SAN DIEGO — On the fourth day of a vicious firestorm, exhausted firefighters and weary residents looked forward today to a break — an expected slackening of the fierce wind that has fanned the state’s explosive wildland blazes.

Forecasters said the Santa Ana wind whipping across Southern California will begin to weaken late this afternoon, followed by cooling sea breezes. The 16 wind-fed wildfires have destroyed nearly 1,300 homes and forced a half-million people to flee.

The shift could allow for a greater aerial assault and help firefighters beat back the most destructive blazes, Homeland Security Secretary Michael Chertoff said during a tour of an evacuation center at Qualcomm Stadium in San Diego.

“If the weather cooperates, maybe we can turn the tide,” he said.

Crews were anticipating an injection of additional firefighters and equipment from other states, mostly throughout the West. Frustration over the firefighting effort began to emerge yesterday when a fire official said not enough had been done to protect homes.

Orange County Fire Chief Chip Prather told reporters that firefighters’ lives were threatened because too few crews were on the ground. He said a quick deployment of aircraft could have corralled a massive blaze near Irvine.

“It is an absolute fact: Had we had more air resources, we would have been able to control this fire,” he said.

The fires have burned 410,000 acres, or about 640 square miles, causing at least $100 million in damage. Twenty-one firefighters and at least 24 others have been injured. One person was killed by the flames, and the San Diego medical examiner’s officer listed four other deaths as connected to the blazes.