SAN DIEGO — Gov. Arnold Schwarzenegger signed an executive order Wednesday boosting the number of wildland firefighters across Southern California in preparation for what he said could be an "extreme" fire season.

Four firefighters will staff each of 53 California Department of Forestry and Fire Protection engines in Riverside, San Bernardino and San Diego counties during the highest fire threat periods.

The department will base a helicopter in San Diego County, site of some of the most severe fires two years ago, and is adding four Conservation Camp fire crews in the southern state. He also pledged to increase state resources as needed to aid Los Angeles, Ventura and Orange counties.

"We face extreme fire conditions in our state with summer heat, high winds, steep mountains and trees everywhere," said Schwarzenegger. He recalled touring the region's devastating fires two years ago after he was elected but before he took office.

Schwarzenegger's current budget includes money for 60 new fire engines, to replace old fire engines and helicopters, for year-round fire staffing in Southern California, and for better communications equipment.