Wall Street has branded the embattled Seabrook nuclear power plant with one of the worst of financial insults: shaky.

"Seabrook is synonymous with risk," concedes Joe Schell of Kidder Peabody & Co. Inc., the firm underwriting financing for the controversial power plant, a major target of the anti-nuclear movement.

And Susan Linden of Merrill Lynch Pierce Fenner & Smith advises, "It is not a good business risk; New England needs power but that need doesn't mitigate the risk."

Through nearly a decade of bureaucratic wrangling, protests and financial handwringing, the project has survived with nearly 20 percent of the 2.300-megawatt twin reactors completed.

Now, with skyrocketing costs and financial problems threatenting the $2.6 billion project, the plant's builders are girding for what may be the final showdown over money.

And the nation's financial community has pegged the state of Massachusetts as the last battlefield in the fight on whether Seabrook will be completed.

"It is possible that if the Massachusetts Utility Commission prohibits the entry of Massachusetts companies into the Seabrook project, Seabrook could be canceled," said Joseph Egan of Merrill Lynch.

Adds Schell of Kidder Peabody, "Massachusetts is critical."

Public Services Co. of New Hampshire, a private utility with a 50 percent stake, is building Seabrook.

Public Service is banking on Massachusetts utilities to drag it out of a fiscal quagmire created by Seabrook. The firm has been told by Wall Street to sell nearly half of its 50 percent interest in the plant or the flow of construction money will be shut off. Public Service would end up with a 28 percent interest.

"I wouldn't describe the situation as rosy," said a usually optimistic Gordon McKenney of Public Service. "We have some tough months ahead; it hasn't been an easy road and it won't be until we stop paying for half the financing of Seabrook.

"But somehow Seabrook will be built for New England and you can put that to bed right now," he said. "We can go out to other utilities in New England -- we will have no trouble finding buyers."

However, in Connecticut, the Millstone III power plant is in jeopardy, the Montague plant and Pilgrim II in Massachusetts have cloudy futures, Jamesport I and II on Long Island have run into serious regulatory trouble and Charlestown I and II in Rhode Island have been virtually scrapped.

In New Hampshire, voters gave Public Service Co. and its loudest spokesman, then-Governor Meldrim Thomson, the brush-off at the polls last fall and the legislature recently outlawed a 9 percent utility surcharge on electric bills that had been used to pay for Seabrook construction.

And last month the New Hampshire Public Utilities Commission questioned Public Service's financial planning and ruled it could sell only three-quarters of the amount demanded by Wall Street. Hearings will be held this month on the difference.

In Vermont, the Public Utilities Commission last week gave power companies in that state permission to buy an additional 2 percent of Seabrook but said the stockholders must assume the full risk -- not the public.

And in Connecticut, the Public Utilities Control Authority strongly suggested that Connecticut Light and Power sell its 12 percent share of Seabrook and United Illuminating divest half of its 20 percent interest.

But while private utilities are clamoring to dump their shares in Seabrook -- 44 percent of the plant is up for sale -- one utility from Massachusetts has developed a fondness for the plant.

The public utility is called MMWEC, which stands for Massachusetts Municipal Wholesale Electric Co. It represents 31 cities and towns in the Bay State -- most of which may not need more power, according to critics.

To Public Service Co., it was corporate love at first sight -- a public utility that already owns about 6 percent of Seabrook and can float taxfree bonds to pay to finish Seabrook.

But Massachusetts state Rep. Lawrence Alexander says: "I question the propriety of using public money to help bail out a private utility."

Merrill Lynch's Linden, who studied the deal, adds: "Public Service Co. is just trying to dump its financial obligation on someone else."

The Massachusetts attorney general's office is fighting the proposed $625 million deal to buy 14 percent more of Seabrook.

There is other opposition.

A grass-roots group called Municipal Power Advocacy Coalition has sprung up to fight MMWEC and an unusual coalition has emerged pitting conservative businessmen, legislators, environmentalists and old line antinuclear power demonstrators from the Clamshell Alliance against the public utility.

The group has achieved its first series of victories recently with the towns of Ipswich, Marblehead and Braintree rejecting offers to buy more power, and opposition is mounting in many of the other towns participating in MMWEC.

"The townspeople and Massachusetts legislators are being duped," replies Public Service Co.'s McKenney. "This is the work of the antinukes who are promulgating antinuclear propaganda to kill Seabrook; they'll do anything to stop Seabrook."

And MMWEC's Tom Roger waves off Rep. Alexander's warning that investing in Seabrook is "throwing good money after bad."

"The only risk is not having the power capacity or burning an additional 10 million barrels of oil a year," said Roger. "If there is no Seabrook by 1985 there will be electricity rationing and rotating blackouts and brownouts and the cost of power will double."

And he says if the project is really in financial jeopardy there are a couple of aces in the hole.

"Every major utility in New England is an owner in Seabrook and before the project would stop and incur billions of dollars in loss, I would think everybody would reach in and buy some more of Seabrook," he said.

"The stakes are very high."

In fact, the stakes are so high, he said, that "the federal government desperately needs Seabrook to carry through President Carter's energy program to break the reliance on imported oil in New England."

"If individual states jeopardize Seabrook," said Roger, "the federal government will take them on."