Conservation groups are closing in on their goal to permanently protect more than 42,500 acres in central Maine that a federal report ranked as one of the nation’s most threatened watersheds.

For the second time this year, Congress appears poised to approve multimillion dollar grants from the U.S. Forest Service’s Forest Legacy program to help protect the largest, unfragmented tract of forest in central Maine.

The full U.S. House of Representatives approved a Department of the Interior budget bill that contains $3.3 million for what is known as the Lower Penobscot Forest project. The Senate is expected soon to take up its version of the Interior budget bill, which also contains $3.3 million for the project.

The money will help the state and several conservation groups prohibit development on more than 42,500 acres in Penobscot and Hancock counties stretching from the Sunkhaze Meadows National Wildlife Refuge in Milford to Great Pond and the west branch of the Union River in the east.

The acreage is part of a landscape the U.S. Forest Service ranked as the country’s No. 1 watershed threatened by development.

Roughly 24,500 acres would remain in private hands, but the Maine Department of Conservation would hold a working forest easement on the land that prohibits development and guarantees public access.

The Nature Conservancy will manage more than 12,700 acres just to the east of Sunkhaze as an ecological reserve.

Earlier this year, Congress appropriated $2.2 million from the Forest Legacy program to help buy about 5,000 acres near the Hancock County town of Amherst that is also part of the Lower Penobscot Forest.

“This actually gives us exactly what we asked for, which is $5.5 million,” said Alan Hutchinson, executive director of the Forest Society of Maine, one of the groups instrumental in crafting the conservation deal. “So this is just fantastic.”

Hutchinson said his organization and the state have to raise approximately $500,000 from private donors to complete the 5,000-acre Amherst deal.

The Forest Society of Maine also is meeting with Amherst officials to work out how the town can be actively involved in managing the land with the state.

“We think it’s a model that might play out in other towns,” Hutchinson said.

When combined with the Sunkhaze refuge and the Department of Conservation’s Bradley and Greenfield units, the Lower Penobscot Forest project will create a corridor of interconnected conservation land totaling more than 63,000 acres.

“This project is a priority for Maine and the U.S. Forest Service,” U.S. Rep. Mike Michaud, D-2nd Congressional District, said in a statement announcing House passage of the budget bill containing Forest Legacy funds.

“It will support the ecosystem of the greater Sunkhaze Meadows National Wildlife Refuge area by promoting sustainable forestry. The project also preserves recreational access so that Mainers can continue to enjoy this environmentally significant and beautiful landscape.”