The Massachusetts Attorney General, an opponent of the controversial Seabrook nuclear power plant, filed suit Friday against the Coalition for Reliable Energy, charging that the pro-Seabrook alliance engages in "deceptive" advertising practices.

In response, the Coalition maintains that Attorney General James Shannon's charges are an infringement of the Constitutional rights of free speech.

The suit is just the latest salvo in an ongoing controversy between the state and proponents of Seabrook. Last week, Massachusetts Gov. Michael S. Dukakis said he would fight the opening of the New Hampshire plant despite a proposal by the Nuclear Regulatory Commission that frees the way for the owners of Seabrook to get evacuation plans approved without state input.

In the suit, Shannon has charged that the Coalition's televised advertisements are unclear and erroneous, said his spokesman Brian McCarthy.

"The attorney general wants it made clear that the group is not a spontaneous, upsurge for the people. It's funding for Seabrook," McCarthy said. "It's deceptive for them to pretend they're something other than advertising for the Seabrook nuclear power plant."

Shannon said that the ads present incorrect information because they "claim that the public will pay for Seabrook whether or not it will go on the line," McCarthy said. "This points is not true, and the owners know that."

Coalition spokesman Cheryl P. Marsh called Shannon's charges of deception "unfounded."

"I don't think we're misleading the public," said Marsh, citing that "more than 12,000 citizens wrote to the Coalition saying they believe in Seabrook."

McCarthy said the Coalition's ads "evolved" from promoting all energy sources to advertising mainly for the opening of Seabrook.

But Marsh said that only the latest of the organization's five televised ads--whose purpose she said is to "educate New England on the impending need for energy sources"-- mentions Seabrook.

She said the nuclear plant is in the ad for a purpose. "The last ad mentions Seabrook because we're facing a crisis," Marsh said. "If Seabrook doesn't come on the line, we're going to be facing a serious energy shortage. Seabrook is ready to go, and we need the power. The only thing we have now is Seabrook."

Seabrook, originally scheduled to start operating in 1981, was initially delayed because of financial problems, but is currently being held-up because of the refusal by Dukakis to submit the evacuation plans necessary to start operating the plant.

Seabrook managers said yesterday that they want to start operating the plant, which cost $4.5 billion and has been opposed by near-by Massachusetts residents who fear nuclear accidents, by the beginning of the summer.

Anti-nuclear groups meanwhile plan to protest and lobby in an effort to prevent the operation of Seabrook. Concord'sSeacoast Clamshell, an anti-nuclear organization,plans to hold a candlelight vigil next month atthe gates of Seabrook to commemorate the Chernobylnuclear accident, said Clamshell member PaulGunter