The U.S. Army Corps of Engineers, responding to Sen. Chuck Schumer’s demand to release its storm-protection plan for Suffolk, on Wednesday revealed the cost had soared to $1 billion.

That is a 33 percent increase from the $750 million that was projected and that Schumer persuaded Congress to include in the relief bill for superstorm Sandy.

An Army Corps spokesman did not respond to questions about the $250 million increase.

Three years ago, the agency proposed spending about $500 million to elevate 4,400 homes located in 2-, 6- and 10-year flood plains on Suffolk’s South Shore.

A few dozen roads would be turned into dikes, by elevating them, and critical infrastructure, such as utilities, would be shielded, the proposal said.

The agency’s proposal for the 83-mile stretch from Fire Island to Montauk Point, known as FIMP, also earmarked $60 million to recreate wetlands to defend against storm surges.

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Another $140 million was set aside for new dunes for Fire Island, but that work was fast-tracked and now is expected to cost $207 million.

FIMP was first put forward in the 1960s.

Like countless other U.S. flood-control projects, it lingered on the agency’s $60 billion backlog — many times the size of its annual $4.7 billion budget — until Sandy struck.

Once Congress approved funding, the Army Corps said it would issue the draft report this winter; it later said it would be released this spring, but missed that deadline.

On Wednesday, the Army Corps complied with Schumer’s demands, promising to publish its draft plan next month and hold hearings in August.

“Long Islanders, some of whom are still feeling the devastating impact of Superstorm Sandy, are tired of waiting on the Army Corps to share essential details on the FIMP resiliency project being planned in their community,” Schumer said in a statement.

“Public meetings will allow residents to voice their concerns, improve the plan and ask important questions that affect their future,” he added.

Army Corps spokesman James D’Ambrosio in a statement said the agency was finishing its internal reviews.

“FIMP is an extremely large, challenging project — over $1 billion with many different components spread over 126 square miles, impacting hundreds of thousands of people so we want to make sure we get it right,” he said.

New York State, the agency’s partner, had no immediate comment. Nor did Suffolk, which is the state’s partner.

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Though the Army Corps in 2013 did not disclose specific locations for elevating homes, it focused on areas bordering bays and inlets, including Babylon, Brookhaven, Copiague, Lindenhurst, Mastic Beach, Patchogue, Southampton, Westhampton, West Islip and West Sayville.

The Army Corps also must go through the environmental impact statement process, which should start after the draft plan is released.

The FIMP project cannot be finalized until the agency has analyzed and responded to all the public comments it receives.