Only a handful of the hundreds of wildfires that have charred at least 4.1 million acres in the West this summer are still out of control, and more than half the estimated 30,000 firefighters who once battled the blazes have gone home.

None of the current fires is posing imminent danger now that autumn has officially started and much of the West has been dampened by fall storms, officials said Thursday."Activity is slacking off considerably now that we have no shortages of resources or people," said Frank Carroll of the Boise Interagency Fire Center. "We still have about 12,000 firefighters in the field, but we are rapidly demobilizing many of them. It's definitely on the downhill slide."

At the height of the fires, about 30,000 firefighters and support people were working on blazes that have caused at least $300 million damage, destroyed hundreds of homes and cost at least eight lives.

The only major fires still out of control are burning in California and Yellowstone National Park.

An arson fire is still burning over 27,000 acres of brushland north and west of Vacaville, Calif., a city of 65,000 people 50 miles northeast of San Francisco.

The fire has destroyed seven homes and 11 other structures. Firefighters said they expect to complete the fireline Friday night and have the blaze controlled Saturday night.

There was virtually no wind Thursday in contrast to 50 mph gusts that fanned the blaze out of control earlier in the week.

Gov. George Deukmejian asked President Reagan to declare four California counties disaster areas.