Thousands of antinuclear protesters packet up their tents and "no nuke" signs yesterday and quietly left the city dump of this old coastal village that has been their home for the last three days.

The last group of protesters marched off the site of what they claimed to be the largest antinuclear demonstration in U.S. history at 3 p.m. after Gov. Meldrim Thomson Jr. inspected it.

A spokesman for the Clamshell Alliance, a loosely knot coalition of New England antinuclear groups, declared the three-day demonstration "a success beyond our wildest dreams."

"If the governor thinks he can keep pushing this plant, he will run into more political trouble than he can imagine," said Steve Hilgartner. "The plant will never be built."

Thomson, who has been an outspoken proponent of the $2.3 billion nuclear plant here, said the coalition "has experienced what must be to them a very distinct and humiliating defeat."

"Not one minute of construction time was lost during the weekend," he said, adding later, "In New Hampshire, law and order has continued to prevail."

It was a far different ending to the demonstration than a year ago when 1.414 protesters were arrested at the ste of the controversial Seabrook facility, which, if completed, would be the largest nuclear power plant in the nation.

Clamshell Alliance originally planned to stage a similar action this year. But after local residents objected, they negotiated an agreement with State Attorney General Thomas Rath to conduct a peaceful protest in exchange for the state setting aside an 18-acre site for a camp-in, rally and alternative energy fair.

Meanwhile, 156 people arrested Sunday in a protest at the construction site of two nuclear plants near Elma. Wash., were scheduled to be arraigned beginning tomorrow.