It was a journey back in time, the "me-generation's answer to Woodstock and the March on the Pentagon.

Up front on a makeshift stage over-looking the construction site of a $2.3 billion nuclear power plant, the old superheroes of the antiwar movement paraded by: Dr. Benjamin Spock, comedian Dick Gregory, singers Pete Seeger and Arlo Guthrie.

A crowd the police estimated at from 8,000 to 10,000 spread out before them in the hot sun, men wearing long hair and jeans, women in jeans and halter tops.

"No nukes. No nukes. No nukes," they chanted after each speaker left the stage during the day-long rally yesterday, part of a three-day demonstration by the Clamshell Alliance, a loose-knit coalition of antinuclear groups.

It was the largest demonstration to date of the growing strength and appeal of the antinuclear-power movement that has spread across the nation in recent years.

"I think we're seeing the death of the nuclear industry here," said John W. Gofman, a nuclear physicist who became disillusioned with nuclear power after working seven years on a government-sponsored study of radiation dangers. "It shows the government's nuclear energy police isn't playing well in Peoria or anywhere else. Jimmy Carter should get the message."

At a time when the loudest voices of social protest are coming from the political right - in the California tax revolt, the right-to-life fight and efforts to turn back gay rights legislation and stop the Equal Rights Amendment - the antinuclear movement has become the new haven of the political left.

The movement's style, rhetoric, tactics and many of its members are borrowed from the civil rights and antiwar movements of the 1960s.

"It's the same thing. In the first place, it is nuclear danger we're fighting. That was one of the things we were worried about in the Vietnam days," said Spock, the noted pediatrician. "The people here are idealists, loving people committed to nonviolence."

It is an almost all-white, rural-based movement, made up in part of antiwar activists who dropped out of middle-class life during the Vietnam war days and moved to the hills of New England and elsewhere. A few years later, many of them discovered nuclear power plants were going to be built nearby.

And if the three-day demonstration here is an indication, the people involved are older (the average age somewhere between 25 and 35), mellower and more inward directed than the antiwar demonstrators of a few years ago. They are, as author Tom Wolfe has said, the "me-generation."

"Mostly I see this as a time when we are each trying to control our own lives and destiny," said Toni Haver, a former antiwar activists from Quechee, Vt.

first two days of demonstrations in Seabrook, a quiet town of 6,000 located along the New Hampshire coast about 50 miles north of Boston. And at nightfall demonstrators were still arguing about whether some of them would seek a direct confrontation with police today that could result in numerous arrests. The alliance had previously agreed to keep the demonstrations peaceful.

Seabrook became the most visible symbol the antinuclear effort after 1,414 demonstrators, claiming the proposed plant's nuclear waste and fuel would pose a political danger to people and marine life, were arrested on trepass charges 14 months ago.

Construction continues on the power plant, which would the biggest in the country. But the protest attracted nationwide attention and brought the Clamshell Alliance the continued animosity of Gov. Meldrim Thomson and the conservative newspaper at the Manchester Union Leader.

Since then, a host of new regional antinuclear alliances have mushroomed around the county with names like SEA (in New Jersey, Catfish and Conchsheff (in Florida), Sunflower (in Kansas) and Crabshell (in Washington state). A dozen such groups, according to spokesmen here, were staging sympathy protests over the weekend.

The protest rally and energy fair here attracted representatives of almost every left-wing group imaginable, attempting to attach their cause to the anti nuclear effort. "Nuclear power is a feminist and lesbian issue," Laurie Holmes of Boston told the crowd at one point. "The struggle against the rape of our earth by rich, white males is the same struggle as the struggle against the rape of our bodies and the rape of our lives."

But Harvey Wasserman, the alliance's chief theoreticians, said the core of the demonstrators is made up of "people who graduated from the antiwar movement" and moved into the country in the old back-to-earth days only to find themselves living beside proposed power plants.

Wasserman is typical of this group. In 1968, he was cofounder of the Liberation News Service, which distributed news articles to the then large underground press. After a year in business, the group broke up and Wasserman moved with one of its factions to a communal farm near Montague, Mass. In 1973 a nuclear power plant was announced for nearby and he and others began efforts to oppose it.

Other nuclear protesters, he said, are attracted by the Clamshell Alliance's nonviolent philosophy and a "feeling of camaraderie and good vibrations."

A number of them called the Willow Rut Affinity Group from Lebanon, N.H., may be typical. They are a highly educated group of students, drawn from well-off, middle-class homes. They have chosen to live in the rural areas of Vermont and New Hampshire. Almost all are vegetarians.

"It's a luxury to be able to be concerned about nuclear power," says one, Richard Barrows, who graduated from Dartsmouth last month.