The people who raised the country's environmental consciousness with Earth Day in 1970 have begun planning another nationwide movement for next spring, this one called Sun Day.

Scheduled May 3, 1978, Sun Day will be "a day of celebration for solar energy . . . to educate the public about solar potentials and to help promote an energy transition from petroleum to safe, nonpolluting and decentralized sources," according to the group's fund-raising letter.

Denise Hayes, who coordinated Earth Day as head of the group called Environmental Action, is chairman of the board of Solar Action, the organizing body promoting Sun Day. Coordinators for Sun Day, both Environmental Action veterans and authors in the ecology preservation field, are Peter Harnik and Richard Munson.

Earth Day, on April 22, 1970, "marked the beginning of a new national commitment to environmental quality," said the group's fund-raising letter. "A similar level of public sentiment now exists for a safe, non-polluing and decentralized power system."

Between now and next May, Solar Action plans to work on a nine-point program aimed at promoting interest in renewable energy resources by increased press coverage, citizen self-help program organization, newsletter publication, and lectures. "We need to dispel the myth that solar energy is an 'exotic' technology," the letter said.

On Sun Day, the group hopes to see local fairs, conferences, rallies, teachings and other related actions around the country reminiscent of those that involved several million people on Earth Day.

Suggested by Sen. Gaylord Nelson (D-Wis.), Earth Day involved a cross-section of the country in a bewildering variety of adhoc groups, skits, marches and rallies.

Congress had to close down for the day because so many of its members were off making speeches. There were mock trials of polluters, trash pick-up campaigns, song fests and petitions of every sort. Politicians rode around in electric and methane-powered cars, stockholders disrupted meetings of corporate giants and New York City banned traffic from Fifth Avenue for two hours.

Earth Day spawned slogans and was taken up by all sides of the political spectrum. Signs condemned "the effluent society" while the Daughters of the American Revolution attacked "pollution of the mind" by communism and church groups condemned polluted spirits.

An estimated 2,000 colleges, 2,000 community groups and 1,000 high schools took part, but many of the days initiatives were shortlived. Groups formed and most of them vanished: "Youth Uncovering Krud" (YUK) in Haverford. Pa.; "Students Concerned About a Revaged Environment (SCARE)" in Cloquet, Minn.; and various groups called GASP.

In the aftermath of Earth Day, some of its own organizers said it had been largely "media hype" and had not gone on to involve segments of society that were not white, well-educated, middle-class and young.

Hayes and others still involved in the environmental movement, however, point to subsequent legislation for clean air, water and environmental impact statements as part of Earth Day's legacy. "The whole issue is now part of the political dialogue of the country." Sen, Nelson said last year. Workers in his office said they knew nothing of the plans for Sun Day, however.

Solar Action has enlisted 18 board members so far including Mayor Thomas Bradley of Los Angeles, Jeremy Stone of the Federation of American Scientist and Michael of McCloskey, executive director of the Sierra Club. Nine staff members will be hired in October and November to put out the newsletter and organize regional offices. "We're ready to take the wraps off and get moving," Hayes said "May is not that far away."