Long accused of being the bastion of upper-class elitism, the strong environmental movement centered here is developing grass-roots strength in the traditionally conservative rural areas of the state.

Local environmental groups, supported by the San Francisco-based Friends of the Earth and the Sierra Club, have won battles in rural counties once considered hostile territory.

One of the most important changes has occurred in the attitude of residents of rural areas. Many now believe that they can stand up to powerful interests and defeat them. For example:

In Sierra County, local environmentalists beat back a proposed $80 million resort by Walt Disney Productions. And in Mendocino County, in northern California's rich timber country, voters imposed strict controls on aerial spraying of pesticides by lumber interests.

In the wake of the Three Mile Island nuclear accident, some environmental leaders believe, there is a increasing skepticism about local governmental officials and business interests in traditionally conservative areas.

"You have to be willing to expand," said Jeanette Anderson, director of the Conservation Training Network (CTN), an ecology-oriented organizing project that is active in rural northern California. "You have to stop talking to yourself. It's no good to have a strong opinion; you have to do something."

CTN, run out of a small office in the Friends of the Earth headquarters in San Francisco, has been offering organizing workshops to local residents in some of California's main anti-environmentalist areas. By providing training in polling, political organizing and media relations, CTN claims to have played a major role in several unprecedented environmentalist victories in several rural northern counties.

Perhaps the most surprising victory in recent months was the successful campaign in June in Mendocino County, 100 miles north of San Francisco, to ban aerial spraying of certain herbicides by timber interests.

"People don't like to see their local resources harmed," said Francia Welker, a Mendocino County attorney and a leader of the herbicide fight. "It's not just a matter of rich people in San Francisco wanting to keep their views; it's a matter of survival. When you realize that the stuff is coming down from the sky and getting into the water supply, you want to do something."

Even representatives of the local timber industry admit that the herbicide vote -- over 50 percent in favor of the ban -- signals a significant shift in local opinion on issues affecting the environment. Long the dominant force in Mendocino County, timber executives believe the local environmentalists, in recent years, have become their equals in the use of political power.

"I think a real rise in their potency has taken place and now it's an even-up situation out here," said John MacGregor, general manager of the Western Lumber Division of the Chicago-based Masonite Corp. "The timber industry, from now on, will win some and lose some."

Some environmental leaders claim they are developing a permanent constituency in rural areas as new arrivals, escaping the ecological problems of the city, join longtime residents to preserve the relatively undisturbed countryside.

"You have a lot of peole out there with small stores and farms who are now fighting the big timber companies, the big forces," said Carl Pope, associate conservation director of the Sierra Club. "They still don't want the government around but they are now attacking all forms of bigness. It's a rejection of post-industrial values and an assertion of very traditional American values -- values which have gone underground for a long time."

The most important attitude change in rural California, Pope believes, has come in the local residents' belief that they can stand up to powerful interests and defeat them. One dramatic example of this, he says, occurred in Sierra County, 300 miles from San Francisco, where a handful of local residents prevented construction of a proposed $80 million resort by Walt Disney Productions.

The resort, which would have attracted an estimated 3 million visitors a year to a county with 3,000 year-round residents, has been staunchly opposed by local activists aided by CTN and other environmental organizations. In March 1978, Disney, frustrated by the opposition and delays in getting approval for the project, pulled out of the county.

"In a tiny county they told us we can't fight that big corporation," said Anne Clark Eldred, a Sierra County environmentalist leader. "You can't fight big money and corporations, they said. But we found we could do it."

Similarly, California's antinuclear movement has been expanding its base in the predominantly rural areas near the unlicensed Diablo Canyon nuclear plant, according to representatives of the Abalone Alliance, a coalition of state antinuclear groups. In recent years the alliance has had little success in developing widespread local support for the drive to block licensing of the plant on a scenic coastal site in San Luis Obispo County, midway between San Francisco and Los Angeles.

Last year the Abalone Alliance rallied 5,000 activists, most imported from urban areas, and tried to blockade Diablo Canyon, resulting in the arrests of 487 persons. The demonstration captured headlines but annoyed many in San Luis Obispo County, which had to pay the bill to police the demonstration and incarcerate lawbreakers.

This year, the alliance, taking advantage of the aftershock of the Three Mile Island nuclear power plant accident March 28, concentrated on winning local support and settled for a peaceful rally June 30. It was attended by Gov. Edmund G. (Jerry) Brown Jr. and an estimated 20,000 others, many of whom, according to alliance leaders, came from the vicinity.

Harold Miossi, a critic of the alliance and descendant of one of the region's most prominent ranch families, believes the change in tactics won friends for the antinuclear movement. A year ago most local residents favored the plant and opposed the demonstrators, but Miossi now believes public opinion is moving in a new direction.

"The community has always been very much concerned with balancing the need for energy and jobs with the need for safety," Miossi said. "But now I would say 75 percent of the people here would rather not have the plant in San Luis. The thing is really turning dramatically out here."