THE CHAIRMAN of the state Public Utilities Commission termed it "a little like Richard Nixon's recognizing China." Environmentalists are calling it "a historic moment," and the head of the California Energy Commission says it is a "bold, clear move . . . [that] is going to shake up some stodgy utilities in other parts of the nation." "It" is the announcement of a dramatic shift in policy by Southern California Edison, one of the country's leading utilities.

Edison, which serves a growing part of the country, expects a 40 percent increase in demand for its electricity by 1990. To meet that need, it has two large nuclear projects nearing completion. Until two weeks ago, the utility had insisted that most of the remaining two-thirds of the necessary new capacity had to come from traditional energy sources, including two huge and controversial coal projects. Edison maintained that no more than 10 percent of its new supply could come from alternative energy sources, including conservation and renewable technologies.

In the course of routine licensing hearings for the new plants, the Environmental Defense Fund produced a detailed analysis showing, it said, that a combination of conservation and alternative sources could produce more energy at far less cost than the coal plants. A few months ago, an independent study by the Interior Department's Bureau of Land Management reached the same conclusion. Suddenly, about two weeks ago, Edison announced a major policy change "to make renewable our preferred technology -- to make it happen."

According to Edison's new plan, nearly two million kilowatts, almost as much as is expected from the new nuclear plants, will be derived from wind, geothermal, solar, fuel cell and hydroelectric sources, and from cogeneration, one of the most promising conservation technologies. Planning for the new coal projects will continue, but Edison's own numbers indicate that the company expects eventually to drop one or both of them -- assuming, of course, that the renewable resources perform as expected.

Edison attributed its change of mind to "some significant successes in a number of research and development areas." It seems equally likely that the utility also took a second look at such things as the skyrocketing costs of capital financing, the declining demand for electricity and the realistic technical potential of new energy sources. The hazards and delays of the regulatory process for large coal or nuclear plants, and the 10 years it now takes to build a new one (as compared with the two or three years required to build a smaller windmill or geothermal facility), must also have been powerful influences.

Regardless of the reasons for it, Edison's commitment is a courageous and welcome change of course. It should mean lower energy costs and less environmental damage for citizens of southern California. More important for the rest of the country, it may well have a greater impact on other utilities' thinking and planning than all the government and academic studies combined.