With thunderous chants of "No More Harrisburgs" and "No Nukes, No Nukes," a vast crowd of at least 65,000 protesters reminiscent of antiwar throngs of a decade ago marched on the Capitol yesterday, calling for an end to U.S. decpendece on nuclear energy.

As their banners billowed under bright skies, the protesters stepped in massive ranks from the ellipse, near the white house, down Pennsylvania Avenue to the west steps of the capitol.

There, they cheered speaker after speaker, including California Gov. Jerry Brown, consumer advocate Ralph Nader, actress Jane Fonda and longtime political activist Tom Hayden.

Triggered by the three mile island nuclear plant accident near Harrisburg, Pa., five weeks ago, the outpouring marked the largest national protest to date by the growing anitnuclear movement.

Police estimated the crowd at 65,000 to 75,000. Organizers of the protest, an umbrella organization of antinuclear, enviromental and other groups called the May 8 coalition, put the figure at "a minimum of 125,000."

Whatever the size, it rivaled the largest demonstrations of the 1970s in Washington, including last summer's women's March for the equal rights amendment.

The crowd, overwhelmingly young, white and middle class, was in good spirits, and there were few incidents. No arrests were reported.

Reliance on nuclear power is a "pathological addiction," boomed Gov. Brown to the crowd, "storing up for generations to come evils and risks that the human mind can barely grasp."

President Carter "betrayed us" when he appointed James Schlesinger as energy secretary, Nader said to cheers.

If Carter does not replace Schlesinger, "then he himself will be replaced in 1980, and that is a fact," Fonda shouted.

Hayden, Fonda's husband, said Carter has a "nuclear energy mentality" that is "eclipsing and destroying his Christian" philosophy.

Robert Pollard, a former safety engineering who resigned from the Nuclear Regulatory Commission staff in 1976 said the NRC "rountinely puts the financial interests of the nuclear industry ahead of your safety."

Protest organizers invited President Carter to address the rally but said that he declined. In his only comment about the protest, Carter said yesterday, "I think it is a legitimate demonstration. I understand the concern about nuclear power, and we're doing all we can to reassure people . . . that what nuclear recators we do have are safe."

Other speakers, ranging from a pregnant woman evacuated from the Three Mile Island area to a war veteran with cancer who was exposed to radiation in nuclear weapons tests in the pacific 20 years ago, flatly laid the blame for nuclear accidents and exposure on the federal government.

It was day filled with protest, but also with suggestion for the future. Speakers urged diversion of U.S. and private research money to development solar, wind, geothermal and other alternative energy sourves.

"Sun, Wind, Water-Let it Flow," said a huge sign in the parade down Pennsylvania Avenue.

"I call on President Carter to pass a law requiring every new house to be built with solar energy," pediatrician and radiation expert Helen Caldcott told the crowd at the Capitol to cheers.

After a morning rally on the Ellipse, the antinuclear marchers moved down Pennsylvania Avenue at noon, led by comedian Dick Gregory, baby doctor Benjamin Spock, feminist leader Bella Abzug, and others carrying a mock coffin filled with "dead" babies.

Immediately behind them was a line of children linked arm in arm and chanting "Hell no, we won't glow" and "Two, four, six, eight, we don't want to radiate." Bright yellow helium balloons sailed over Pennyvylvania Avenue.

Deputy Chief Hugh Groves of the U.S. Park Police said the 65,000 crowd figure was based on joint estimates made by Park, Capitol and D.C. police. Capitol Police Chief James Powell put the figure at 65,000 to 75,000.

As speaker followed speaker at the Capitol, the crowd lolled and picnicked in the afternoon sun. Beer and wine flowed freely, and the sharp fragrance of marijuana floated occasionally across parts of the crowd.

The crowd was an amalgam of American activists-suburban liberals, Democrats, Republicans, assorted Socialists and a few Communists.

Some youhts, apparently unpoliticized, came primarily to party-to relax, smoke, drink, listen to the music and speeches from the rostrum. The day was mellow with few hassles.

Susan Cassidy, the 22-year-old pregnant woman from Middletown, Pa., adjacent to the Three Mile Island nuclear plant, told the crowd she was "overwhelmed with anxiety" when she was evacuated from the area after the accident on March 28, and has been "too frightened to return" ever since.

"No one should have to live through what my family has experienced," she said.

Orville Kelly, a veteran who said he underwent nuclear weapons testing exercise on the Pacific island of Eniwetok in the late 1950s, said he has incurable cancer resulting from the exercises. He said he has received no compensation from the government.

Protest organizers said the theme of yesterday's demonstration was "No More Harrisburgs"-a purposefully generalized slogan to satisfy the broad-based coalition of the 200 groups involved in putting the protest together.

"Some groups want an immediate, total shutdown of all nuclear plants," said coalition spokesman Tim Massad.

"Wome prefer a phaseout to reduce the economic shock, and others want a moratorium until further health and hazard studies are done."

Coalition cooradinator Don Ross said yesterday's protest also brought together for the first time the "young grass roots activists who have been demonstrating at nuclear sites and the scientists, lawyers and others here in Washington" who are lobbying for legislative and White House policy changes.

"Our purpose," Massad said "is to demonstrate the mounting opposition to nuclear power and to focus on Carter, Schlesinger and Congress as responsible for such things as the Three Mile Island accident.

Massad and other coalition spokesmen acknowledged that the movement, while growing, has so far attracted few minorities and rank-and-file labor union memebers-much as the antiwar movement a decade ago failed to do.

The coalition did receive the endorsement of several union locals, and William Winpisinger, president of the 960,000-member International Association of Machinists, addressed the crowd at the Capitol, calling for control of spreading nucear power. CAPTION: Picture 1, With the Capitol in the background, a portion of the crowd estimated at 65,000 settles in by the west steps to hear speeches opposing the United States dependence on nuclear nower. By Frank Johnston-The Washington Post; Picture 2, Reminiscent of the antiwar gatherings of the '60s, this crowd gathered at the Capitol yesterday to protest U.S. dependence on nuclear energy.Captiol police estimated the throng at 65,000 to 75,000. By Larry Morris-The Washington Post; Picture 3, A person represnting the Man of Death from Nuclear. Radiation demonstrates near the Capitol yesterday. By Frank Johnston-The Washington Post