New York State plans to take legal action if the U.S. Environmental Protection Agency finalizes a proposal to dump what critics have called potentially harmful sludge in the eastern Long Island Sound, Gov. Andrew M. Cuomo’s chief legal counsel said Saturday.

The attorney, Alphonso David, said Cuomo’s office would ask a federal judge to stop the EPA from implementing the plan, or from issuing permits for the dumping of the sludge — most of which comes from Connecticut and is being dredged as part of a major project by the U.S. Army Corps of Engineers.

“We’re putting the EPA on notice that if they finalize this rule, we will immediately commence litigation to stop it,” David said. “Our position is that the Long Island Sound should not be a waste disposal.”

Harbors and ports need to be dredged to allow boats, cargo ships and passenger liners to pass safely. But at issue has been where to put the dredged sediment and how to handle the cost of different disposal methods.

Since the 1980s, the dredged sediment have been dumped at four open-water disposal sites in the Sound. Permits for two locations, Cornfield Shoals and New London, in the eastern region of the Sound, expire Dec. 23.

The EPA has said the existing disposal sites don’t have the capacity to handle the anticipated volume of sludge over the next 30 years — hence the need to create an additional dumping site in the eastern Long Island Sound.

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The agency is expected to issue a final decision on the proposed dumping site later this year.

The Department of State, which governs the coast, and the Department of Environmental Conservation already are on record opposing the plan, which also has been criticized by a number of local environmental activists and politicians, including Rep. Lee Zeldin (R-Shirley).

David said the legal challenge would likely mark the first time New York has sued the federal government over sludge-dumping in the state.

The state’s potential challenge to the dumping plan might involve an argument that it is “arbitrary and capricious,” and violates both state and federal law, David said.

An EPA spokeswoman did not immediately comment Saturday on the state’s threat of legal action.

The EPA has said open-water disposal of sludge is safe. But sludge pulled from the bottom of rivers, lakes and harbors can contain mercury, lead and pesticides, and is harmful to marine life, according to environmentalists and critics like Zeldin, who had urged federal officials to instead recycle the material or dispose of it on land.

“We will do everything in our power” to prevent dumping in the eastern Sound, David said.