WISCASSET – An environmental critic of a proposed $1.5 billion energy plant that would burn gas extracted from coal challenged claims that the project would boost efforts to curb global warming.

“This will be a step backward in our attempts to lower greenhouse gases,” Steven Hinchman, staff attorney for the Conservation Law Foundation, said Tuesday night at a public meeting on the Twin River Energy Center project.

The plant, to be built on the site of the former Maine Yankee nuclear power plant, would use coal and wood biomass to produce electricity and diesel fuel.

Hinchman took issue with a claim by Scott Houldin, Point East’s project manager, that the type of clean diesel fuel produced at the site would help address the global warming issue.

“Studies show the process works when you make diesel fuel out of biomass, but not out of coal,” Hinchman said, citing a 2001 Department of Energy report that said making diesel fuel out of coal increases the carbon dioxide footprint.

Houldin said he would bring more information on carbon dioxide tracking to another meeting in two weeks.

Some in the crowd of about 100 welcomed the project.

“I think it’s a wonderful thing that you’re putting that land to use,” said Katherine Martin Savage, a former selectwoman. “It couldn’t be any better for the town.”

But Dennis Dunbar of Westport Island raised the issue of the plant’s height and its visual impact.

“I’m concerned about the loss of property values for those of us who live nearby,” he said. “The skyline of such a plant, the lights all night, that could reduce the value of my home by up to 50 percent.”

Houldin emphasized that the project would not go forward without support from the town.

“This is an opportunity,” he said. “And we need to know how you feel about it before we proceed.”

Houldin said Point East expects the permitting process to take two years and construction to take another four years, putting the target date for completion of the plant at 2013.

Rep. Peter Rines, D-Wiscasset, said after the meeting that the state could use more diversity in its fuel sources. “Maine’s energy portfolio is too dependent on natural gas,” he said. “This certainly would be a step in the right direction.”