A plane drops fire retardant over a wildfire as clouds of smoke billow behind and above Saturday, July 19, 2014, near Carlton, Wash. A wind-driven, lightning-caused wildfire racing through rural north-central Washington destroyed about 100 homes Thursday and Friday, leaving behind solitary brick chimneys and burned-out automobiles as it blackened hundreds of square miles in the scenic Methow Valley northeast of Seattle. (AP Photo/Elaine Thompson)

SEATTLE, Sept 11 (Reuters) - The wildfire season in Washington state has been one of the most destructive on record, charring 550 square miles of wilderness and destroying hundreds of homes and structures, the state Department of Natural Resources said on Thursday.

The assessment came as Washington Governor Jay Inslee renewed a request for the federal government to offer assistance to more than 300 people who lost their homes during July's record-setting Carlton Complex blaze near the Cascade Mountains.

Washington has already spent $81 million battling blazes this year, with a normal operating budget of $25 million annually, said Sandra Kaiser, a spokeswoman for the Washington State Department of Natural Resources.

With unusually destructive wildfire seasons predicted to continue in California, Oregon and Washington amid drought-like conditions, low humidity and warmer than average weather, Kaiser said, the priority should be shifting funds to fire prevention.

"The hope is that we can do a better job of preventing fires so we don't have to spend so much fighting fires," she said.

By the end of August, 363,000 acres, or 550 square miles, had burned, compared with an average of 61,000 acres over the past five years.

Kaiser said 2014 was likely to end up the most costly and destructive wildfire season on record.

On Wednesday, state forecaster Aaron Everett told a panel of lawmakers Washington would benefit from putting more funds toward preventative measures including thinning trees in parched forests and helping homeowners prepare in the event of a wildfire.

Experts are also bracing for more fire activity this fall, with September forecasts indicating low humidity, lightning storms and extremely warm weather. (Reporting by Victoria Cavaliere; Editing by Scott Malone and Mohammad Zargham)