A coalition of conservation groups has agreed to pay Plum Creek roughly $35 million to protect permanently more than 340,000 acres of forestland central to the company’s massive Moosehead Lake development plan.

Back in March, Plum Creek Timber Co. officials said they had brokered tentative agreements with three groups to prohibit development on large tracts near Moosehead while guaranteeing public access and sustainable logging on most of the land.

On Tuesday, The Nature Conservancy of Maine, the Appalachian Mountain Club and the Forest Society of Maine released some of the details of the deal, including the $35 million value and the purchase time frame.

Plum Creek officials also said Tuesday they submitted the information to the Land Use Regulation Commission, which now is expected to launch its formal review of the company’s development proposal.

The pact between Plum Creek and the groups, if completed, would stand as one of the largest land conservation agreements in both Maine and national history. But the deal comes with one giant string attached.

The 343,000-acre conservation plan is contingent on Plum Creek receiving state approval for two resorts and nearly 1,000 house lots on or near Moosehead, Maine’s largest lake. The plan is the largest subdivision ever proposed in Maine.

That’s too steep a trade-off for some concerned about the proposed development’s impact on the region’s rural character.

“The very best lands for development are being developed, and the areas that are being conserved are in the backlands,” said Cathy Johnson with the Natural Resources Council of Maine. “It’s the development that people need to be paying attention to and the location of the development.”

The agreement contains three separate components:

. A 270,000-acre conservation easement encompassing mostly forested areas east and west of Moosehead. Plum Creek agreed to sell its development rights on the land to The Nature Conservancy for $10 million, or $37 an acre.

. The sale of 28,320 acres in the Roach Ponds areas to the Appalachian Mountain Club, creating a corridor of conservation land stretching from Baxter State Park to Moosehead.

. The sale of 45,200 acres near the Moose River south of Jackman to The Nature Conservancy.

The combined value of the Roach Ponds and Moose River land sales is $25 million, or about $340 an acre.

“The agreement means we can conserve vast stretches of forest near Moosehead Lake, protecting forest-products jobs, natural resources and public access, including hunting, fishing, hiking, backcountry and motorized use,” Mike Tetreault, executive director of The Nature Conservancy of Maine, said in a statement.

Representatives of the three groups said the negotiated prices were at or below fair market value.

The organizations would have five years from the date of LURC approval to raise the money from private and public sources. Group representatives also pointed out that the contract is binding should LURC approve Plum Creek’s concept plan.

“We will do this,” Nature Conservancy spokesman Bruce Kidman said. “We think we have the track record. And certainly the three organizations working together have the track record to achieve something like this.”

Plum Creek officials also are offering to donate conservation easements on 72,000 acres east of Moosehead to “balance out” the development, as required under LURC’s guidelines for concept plans. The easements would be administered by the Forest Society. Company officials cite the total conservation package – more than 400,000 acres – as proof that they heeded public demand for more permanent conservation in their development proposal.

Not everyone is pleased with the conservation deal, however.

Several organizations, including NRCM, Maine Audubon and the Moosehead Region Futures Committee, have criticized the privately negotiated conservation agreement as irrelevant to LURC’s public review.

NRCM’s Johnson said there are “definitely some good elements” to the conservation deal. But the group remains concerned about some language in the conservation easement, not to mention the “huge amount of development” that will occur if Plum Creek’s plan is approved, she said.

Jim Glavine, vice president of the Moosehead Region Futures Committee, said his group is “delighted” with the amount of proposed conservation. But Glavine said the committee, which was organized to give Moosehead-area residents a greater voice in the debate, still has concerns about the location of conservation and a lack of public input into the deal.

“We want to reserve judgment until we see the document,” Glavine said.

Alan Hutchinson, executive director of the Forest Society of Maine, said the framework is flexible enough to allow for changes during the LURC process.

Both The Nature Conservancy and the Forest Society of Maine are taking no position on Plum Creek’s overall development plans or the location of development. Those are all issues best addressed by LURC, Kidman and Hutchinson said.

The Appalachian Mountain Club has yet to take a position but reserves the right to do so in the future, according to the group’s Maine policy manager, Bryan Wentzell.

LURC director Catherine Carroll said late Tuesday afternoon that she had not seen a copy of the conservation framework. Once LURC staff members receive the information, they likely will deem the application complete and move on to the next step of the review.

Carroll said she hopes to hold the first public hearings on Plum Creek’s plan in May or June.

The three groups’ announcement came one day after NRCM released the results of a survey that the group said indicates strong public opposition to Plum Creek’s proposal.

Fifty percent of those polled said they considered Plum Creek’s plan a “bad idea” compared with only 27 percent who believe it is a “good idea.” In a similar fall 2005 poll, 41 percent said the plan was a bad idea, while 20 percent approved of the concept.