HALLOWELL — Maine’s Public Utilities Commission voted Thursday to grant a key certificate to Central Maine Power’s controversial, 145-mile transmission line through western Maine.

The three commissioners unanimously agreed with a PUC staff report that the economic and grid reliability benefits of CMP’s proposed $1 billion transmission line outweigh harder-to-gauge impacts on scenery and outdoor recreation in the western Maine mountains.

In granting a “certificate of public convenience and necessity” to the New England Clean Energy Connect project, the commission endorsed a settlement agreement that provides $258 million in financial incentives to the state, communities and electric ratepayers in Maine. The decision represents a major, initial victory for CMP and its partner, Hydro-Quebec, on a proposal to build a $1 billion, high-voltage transmission line supplying Massachusetts with renewable energy.

“I think the end result is a good result for Maine ratepayers and a necessary one to continue to meet the energy infrastructure needs of both Maine and the region,” said Commission Chairman Mark Vannoy.

But while a CMP official said the company was “thrilled” by Thursday’s vote, the project is still under review by the Maine Department of Environmental Protection, the Land Use Planning Commission and the federal U.S. Army Corps of Engineers. And the project’s numerous opponents are vowing to fight at every step.

“This ruling was anticipated, and that’s why our thousands-strong volunteer army has been working hard to fight this line at the local level,” Sandi Howard, director of the group Say NO to NECEC, said in a statement. “We are looking to the DEP and LUPC to protect Maine’s environmental interests.”

CMP is seeking authority to built 145 miles of high-voltage lines along a 150-foot-wide corridor stretching from the Maine-Quebec border just north of Coburn Gore to a power station in Lewiston. Along the way, the line would cross under the scenic Kennebec River Gorge but would also cut across the Appalachian Trail as well as lakes, rivers, streams and wetlands all along the corridor.

For supporters, the project offers 1,200 megawatts of clean energy that will bolster Maine’s rural economy, lower electric rates and reduce New England reliance on fossil fuels while combating climate change. For critics, it’s a greedy money grab for foreign developers, etching a 150- to 300-foot-wide scar that would run 53 miles through Maine’s western mountains to help Massachusetts meet its renewable energy goals, while falling short of delivering the promised benefits for Mainers or for the planet.

Critics have seized on those potential aesthetic and environmental impacts to oppose a project that they predict will harm the economy of a rural region heavily dependent on tourism dollars. Additionally, critics question whether the project will dramatically decrease emissions of greenhouse gases tied to climate change.

Vannoy as well as fellow commissioners Bruce Williamson and Randall Davis all acknowledged the project will impact scenery and recreation along the corridor but the benefits outweigh the negatives. But they disagreed with arguments that the project will not reduce greenhouse gas emissions and agreed with PUC staff that CMP has demonstrated sufficient public need or interest to give the project a green light.

“I’ve been camping, fishing, rafting and snowmobiling in the area, including Coburn mountain,” Davis said. “Additionally, based on the pleas at the Forks public hearing to educate myself, I have flown the entire length of the corridor . . . I appreciate the area. I simply do not see the effects using the extreme terms often being used.”

CMP has been losing ground in the public fight over the corridor in recent months as town after town in western Maine voted to oppose and, in multiple instances, rescind previous support for the project. The project received a significant boost in March, however, when CMP, Hydro-Quebec and several parties negotiated a settlement or “stipulation” agreement that sought to sweeten the deal financially for the state.

That package offers $258 million in incentives in the form of lower electric rates, subsidies for heat pumps and electric vehicle charging stations and other concessions. Ratepayers would receive $140 million to lower their bills – but spread over 40 years – while low-income customers would receive an additional $50 million in breaks.

One of the key negotiators on that deal, Maine Public Advocate Barry Hobbins whose office represents ratepayers at PUC proceedings, said the initial offer was “pretty low compared to where it should be.” Reading the tea leaves of the PUC, Hobbins along with the Industrial Energy Consumer Group, the Conservation Law Foundation and the Acadia Center secured an agreement that was crucial in winning Gov. Janet Mills’ support for the project.

“I think we feel good about that for Maine ratepayers,” Hobbins said after Thursday’s vote. “I know that without our efforts and other stakeholders that wouldn’t have occurred. And we would have had a decision that would not have included (the) ratepayer savings.”

In explaining his support, Commissioner Williamson commented that the economic impact of the project “is substantial” even without the stipulation agreement.

But opponents said those financial benefits are minimal when spread over 40 years and do not make up for the impacts to western Maine’s scenery, wildlife and tourism industry.

Sue Ely, clean energy attorney for the Natural Resources Council of Maine, which is an official intervenor in the regulatory review, said the organization was “deeply disappointed” but not surprised by the PUC decision.

“This is the Public Utilities Commission choosing CMP’s corporate interest over the best interests of Maine and its ratepayers,” Ely said Thursday morning. “The decision is based on CMP’s recital of the facts and it ignores all of the facts brought into the proceedings by all of the intervening parties. And it dramatically overstates the benefits and under-values the harms that will come from the project.”

Nearly three years have passed since Massachusetts enacted a landmark law to solicit large quantities of clean energy to fight climate change and first selected Northern Pass, a project promising to bring a new source of Canadian hydro power to New England. But 14 months ago, New Hampshire’s siting board unexpectedly rejected Northern Pass. That prompted a hasty pivot to CMP’s runner-up proposal, New England Clean Energy Connect, which beat out a third option planned through Vermont.

But by having the PUC permit in hand, CMP can at least aspire to bring the project online as planned in 2022. Thorn Dickinson, vice president with CMP parent company Avangrid Networks, said the company hopes to have all major permits in hand by year’s end so construction can begin.

CMP already owns or has rights to all of the land along the 145-mile corridor in Maine, much of which is commercial forestland.

“We are thrilled with the decision,” Dickinson said. “It’s an 18-month proceeding that looked carefully at all of the issues and confirmed the substantial environmental and economic benefits associated with the project.”

Thursday’s decision by the three commissioners wasn’t a surprise. Two weeks ago, the PUC staff had issued a recommendation reportto the commission, outlining why the project should be approved.

Vannoy said commissioners had to balance the potential impacts with the “significant benefits” to the state. He said those benefits include displacing regional power generation by fossil fuels that pump climate-warming gases into the atmosphere, improved fuel security in New England and providing “a pathway” for additional megawatts at no cost to the state of Maine.

“Any time you have a significant energy infrastructure project there are going to be adverse impacts along a corridor,” Vannoy said. “But we looked at that very carefully. It’s a working forest in that portion of Maine . . . and there are important things that the project is doing, like going under the Kennebec Gorge.”

— Portland Press Herald staff writer Tux Turkel contributed to this story.