PORTLAND, Maine — Maine’s highest court ruled Thursday that regulators were on safe procedural ground when they approved Plum Creek’s Moosehead Lake housing and resort plan, ending one of the costliest and most contentious development battles in state history.

The state supreme court supported the Land Use Regulation Commission’s rezoning of nearly 400,000 acres in the Moosehead region. The concept plan allows Plum Creek to create up to 975 house lots and two large resorts on roughly 16,000 of those acres over the next 30 years.

Plum Creek must receive permits for each subdivision or resort, all but guaranteeing the regulatory skirmishes with opponents are far from complete. But in the immediate future, the court’s ruling will trigger the completion of a conservation deal guaranteeing public access to 363,000 acres of timberland that will remain working forests.

Supporters hope the combination of land conservation and planned development will provide a boost to a region that was struggling with population loss and high unemployment long before the recent recession.

“I don’t think anybody feels that this is a silver bullet,” said Craig Watt, whose family operates Indian Hill Trading Post in Greenville. “But I think a lot of people see this as an opportunity to enhance the economy of the area.”

LURC’s September 2009 vote on the Plum Creek proposal followed a regulatory review involving 300 hours of hearings, millions of dollars in legal fees, and testimony from thousands of citizens passionate about Maine’s fabled North Woods.

Mainers have been deeply divided over Plum Creek’s plan ever since the company unveiled its first proposal nearly seven years ago. While supporters touted the mix of planned development and conservation, opponents predicted the houses, resorts and roads would mar the natural beauty that has drawn tourists to the region for generations.

Three opponents of Plum Creek’s plan — the Natural Resources Council of Maine, RESTORE: The North Woods and the Forest Ecology Network — promptly appealed LURC’s decision.

A Superior Court justice dismissed most of the group’s claims in April 2011 but nonetheless halted the plan after determining LURC violated its own rules by not holding another public hearing before adopting a substantially rewritten rezoning application. He remanded the case back to LURC for additional hearings.

The Supreme Court disagreed Thursday.

“We conclude that LURC did not violate its procedural rules and did not otherwise err by approving the rezoning petition and concept plan,” the court wrote.

Plum Creek officials were pleased to have the option of moving forward 2½ years after LURC approved their concept plan. That green light arrived, however, at an economic time when high-priced lots for vacation homes are not exactly in high demand.

“We believe the Supreme Court’s decision is the final one and the concept plan is in place as of today,” Mark Doty, a spokesman for Plum Creek in Maine, said in an interview.

“Today’s news is great but it is a very long-term plan,” Doty said. “So we will take care of the conservation [plan] and then consider the market conditions for future development opportunities. It’s been a long legal process and we have had our efforts on hold as we awaited the final outcome.”

Out of additional appeal options, Plum Creek’s critics conceded defeat on the concept plan but pledged to stay involved in the permitting process.

“If Plum Creek decides to move forward with its real estate development, it will have to apply for specific permits, and the development would have to be reviewed and approved before construction could begin,” said Lisa Pohlmann, NRCM’s executive director. “We know that many Maine people have expressed concerns about Plum Creek’s development proposal; there will be additional opportunities for public comment if and when the company files permit applications.”

Jym St. Pierre with the Maine chapter of RESTORE worried that the court’s decision could have wider implications both in terms of LURC’s handling of similar proposals and landowners’ expectations when seeking to rezone for subdivisions. St. Pierre said the fact that LURC allowed privately negotiated conservation deals valued at $25 million to be part of the regulatory review process set a “very troubling precedent.”

“We will see whether this decision today is the starting gun for the end of the Moosehead region,” St. Pierre said.

Of course, several prominent conservation groups either supported Plum Creek’s plan or were active participants in the negotiation process.

The Nature Conservancy, for instance, will pay Plum Creek for conservation easements on 266,000 of the 363,000 acres and transfer those easements to the Forest Society of Maine. The Appalachian Mountain Club and The Nature Conservancy purchased another 41,500 acres from Plum Creek as part of the privately negotiated deal.

Mike Tetreault, executive director for The Nature Conservancy in Maine, said the result will be a 2 million-acre conservation corridor stretching from the St. John River to Moosehead and Baxter State Park.

“That’s all in conservation now and it is the size of Yellowstone Park,” Tetreault said.

Gov. Paul LePage, whose administration inherited the Plum Creek court battle, praised the court action.

“This court decision affirms our belief that good land-use planning, conservation easements on working forests and expansion of the eco-economy in the Piscataquis and Somerset counties can be founded on common ground,” LePage said in a statement. “I commend Plum Creek, conservation groups engaged in the easement, LURC, the forest industry and the Greenville community on their achievement.”