Plum Creek Timber Co. has accepted state regulators’ conditions for approving what would be Maine’s largest-ever development — the Seattle-based company’s plan for nearly 1,000 house lots, two large resorts and hundreds of thousands of acres of land conservation in the Moosehead Lake region — and is moving on to the project’s next review phase, officials said Friday.

The Land Use Regulation Commission staff now will craft additional documents outlining the plan’s implementation. The final plan is expected early next year for final approval.

Two opponents of Plum Creek — Maine Audubon and the Natural Resources Council of Maine — said Friday they are exploring ways to legally prevent the project from going forward.

LURC in September gave its approval to Plum Creek’s proposal, including a controversial plan to develop a resort on Lily Bay, an unspoiled area that conservationists wanted left alone.

In accepting LURC’s conditions on the concept plan, Plum Creek’s general counsel wrote that many of the conditions were difficult to accept and would burden the company with additional costs.

At the same time, “we believe the concept plan … is too important to all of us — the state of Maine, the Moosehead region and our company — to abandon our efforts at this point,” James Kraft wrote.

Luke Muzzy, Plum Creek’s project manager, said the company now would await LURC’s recommendations on how the company should implement its plan.

Catherine Carroll, LURC’s executive director, said Friday that the Forest Society of Maine and the Maine Bureau of Parks and Land were the last of the half-dozen or so implementing parties or major players in Plum Creek’s plan to approve changes proposed by LURC.

Those approvals came on or about LURC’s Tuesday approval deadline, Carroll said.

“Everybody has agreed that they can accept the broad recommendations the commission has made,” Carroll said Friday. “This has forwarded everyone along toward eventual approval, but before we can get that we have to get through the tier-2 issues that are in front of us.”

As Carroll described them, tier-2 issues are the detail work and very particular commission recommendations on everything from developing standards for vegetative clearing on development sites to agreements on the language of conservation easements.

She anticipated that staff approvals for these would happen fairly easily with an eventual final vote by LURC coming in the spring.

“I am pleased to see that this process is moving along,” Carroll said. “Right from the get-go, it has been fair, impartial, thorough and transparent. I am pleased to see the parties coming to a place where they can all make this concept plan be consistent with the commission’s rules for allowing concept plans.”

Opponents of Plum Creek’s plan said Friday that LURC blew its chance to protect the Eastern United States’ largest contiguous forestlands and the sensitive, lovely areas within them.

“We recognize that many changes have been made in the proposal over the last three years, but from our position, LURC has failed to address the two big issues,” Jody Jones, a wildlife ecologist for Maine Audubon, said Friday. “The plan proposes too much development, and it’s in places like Lily Bay that are simply inappropriate for development.”

LURC was seduced by the conservation package within Plum Creek’s proposal and that “biased the commissioners into making the plan work,” Jones added.

“Maine people have consistently opposed the amount of development and a number of specific locations that LURC is now set to approve,” said Cathy Johnson, North Woods Project director for the Natural Resources Council of Maine. “This place is too special to let it get sliced and diced into house lots by out-of-state developers like Plum Creek.”

Both organizations said they are pondering various ways to appeal or legally prevent the project.

A final LURC vote on the plan won’t mean the start of construction. The developers still would need to receive a litany of additional approvals and permits before breaking ground on any of the Plum Creek projects.

LURC would be approving a rezoning plan for 975 house lots and two large resorts near Moosehead Lake, Maine’s largest. LURC staff and commissioners have recommended a long list of changes to the plan.

However, the two most contentious aspects of the plan — the total number of house lots and development on Lily Bay — remain in the proposal.

LURC approval also would trigger the permanent conservation of more than 400,000 acres of forestland in the region, which commissioners have said was critical to their endorsement of Plum Creek’s historic development plan.

Plum Creek’s proposal has been controversial since the day it was announced in April 2005. While supporters view the planned growth and resorts as a model for economic revival, opponents predict the development will spoil the natural beauty that draws tourists to the region.

Thousands of people have weighed in on the proposal on all sides.

The Associated Press contributed to this report.