Gov. Meldrim Thomson, a staunch advocate of nuclear power, said he was "disgusted, disappointed and angry" when he heard the news.

Shirley Gustovson, the town clerk in nearby Hampton Falls who has fought the controversial Seabrook nuclear power plant since it was proposed a decade ago, said she just "smiled like a Cheshire cat" when she heard about the Nuclear Regulatory Commission's decision Friday halting construction of the plant while the adequacy of its cooling system and alternative sites are studied.

The decision was touted as a major victory for the burgeoning anti-nuclear power movement by a band of demonstrators who had camped out in front of the NRC's Washington offices for three days last week.

But here in New Hampshire - one of the main battlegrounds in the environmentalists' war against nuclear power - the decision drew a reserved reaction from longtime proponents and protesters, who have seen the regulatory agencies issue conflicting decisions on the Seabrook plant for eight years.

Our jubilation is mixed with reserve because the nuke hasn't been completely stopped; we all understand how the bureaucratic structure works and we realize the decision can still be overturned," said Sharon Tracy, who celebrated the decision over a glass of beer with two other protesters at a bar in Portsmouth. "We can't let our guard down now."

Tracy is an organizer for the Clamshell Alliance, the New England anti-nuclear power coalition that sponsored last weekend's three-day rally of more than 12,000 people on the site of the partially completed $2.3 billion plant here. Last year 1,414 demonstrators were arrested in an illegal "occupation" of the site.

"I just think the decision is bad but they'll probably change it in a few weeks just like they always do," said William Somerby, one of 2,200 workers at the plant whose jobs are in jeopardy because of the NRC ruling.

Public Service Co., the private utility building the plant, had threatened layoffs of up to 1,800 workers if the NRC again halted construction.

"We can probably plan on blackouts, brownouts and rationing of electricity in the early and mid-80s because of this construction halt," said company spokesman Norman Cullerot. He said the twin-reactor 2,300 megawatt unit, originally scheduled for completion by 1981, will probably not be built until close to 1990.

Construction delays will cost the company $500,000 a day, or $15 million a month, because of inflation and interest charges, he said. "And the cost will have to be paid by the citizens of New Hampshire and New England because there are nine other companies with investments in the Seabrook plant."

Gov. Thomson, who is running for a fourth term, said, "We in New Hampshire are going to make an issue out of nuclear power as strongly as the people in California did with Proposition 13. When is this country going to wise up to the fact that we need nuclear energy?"