Several thousands demonstrators rallied here today to support the proposed $2 billion Seabrook nuclear power plant.

Predominantly construction workers and utility company employees from New England and New York, they paraded through downtown Manchester and packed the JFK Coliseum to hear speakers urge a greater voice for nuclear power.

The demonstrators, many wearing hard hats and brandishing colorful pro-nuclear-power signs said the rally was intended to offset the publicity given to anti-nuclear power groups like the Clamshell Alliance.

Over the May 1 weekend, 1.414 Clamshell demonstrators were arrested for trepassing on the proposed Seabrook site.

Construction on the plant has been halted and is awaiting a final approval by the U.S. Nuclear Regulatory Commission. The cooling system was approved last week by the Enviromental Protection Agency, despite contentions that the hot water discharged by the system would harm sea life.

Today's pro-nuclear demonstrators came with the blessings of utility companies throughout New England and New York. Long Island Lighting Co. provided its employees an all-expenses-paid trip to the rally in six air-conditioned buses. Boston Edison also sent a bus from Plymouth, Mass. Both companies have interests in nuclear power plants.

Spokesmen for many other utility companies said they supported the rally but were not actively participating.

A number of construction unions too, provided buses for their members.

Constructions workers said they supported nuclear power because of the need for more jobs and a cheaper source of energy.

James Martin, of the Hampshire County, N.H., Building Trade Council, held a sign reading "Working People Want Seabrook." "I'm here today because my people want to go to work, and I don't want to see them unemployed because that other group of protesters cay yell louder than we can," he said.

Ronald Lajoie of the Providence, R.I., Electrical Workers Union, who came up in a car pool like many of the demonstrators, said, "We need more nuclear power or we won't be able to survive in the next five or 10 years. Our families will starve or freeze to death."

Madeline Thompson, a steamfiters's wife and president of the pro-nuclear New Hampshire Voice of Energy, said she organised this demonstration to "put a face to the hand that's been writing letters to Washington.

"The hand that writes the letters also pulls the lever in the ballot box," she said, "and that is what this rally is really saying."

The crowd's loudest cheers came for New Hampshire Gov. Meldrim Thomson who said, "This is a much better audience than the one I saw the first of May, by comparison, you are beautiful."

In a second reference to the protests at Seabrook Thomson said, "Why should we allow a small minority to bring America to her knees? . . . You've assured that Seabrook will become an accomplished fact and America will be independent of the OPEC countries and not dependent on anyone else."