PORTLAND – A multistate plan is nearing completion that would set limits on carbon dioxide pollution from power plants.

The first-in-the-nation agreement, called the Regional Greenhouse Gas Initiative, would freeze carbon dioxide pollution at current levels through 2015, then require a 10 percent reduction by 2020.

Power generators would have to use cleaner fuels or improve efficiency to stay within the caps, or pay other power plants to make the reductions for them.

Besides Maine, the plan includes New York, Connecticut, Delaware, Massachusetts, New Hampshire, New Jersey, Rhode Island and Vermont. State leaders are scheduled to meet in Rhode Island on Sept. 28 and 29 to sign the agreement.

“We very much support the concept,” said Maine Department of Environmental Protection Commissioner Dawn Gallagher. “We need to make sure Maine is treated fairly.”

When the federal government rejected an international treaty to restrict carbon dioxide emissions from power plants, the northeastern governors decided to create regional rules that would put the states in step with Canada, Europe and other parts of the world.

Discussions have been ongoing for two years and have included state officials, energy producers, environmentalists and consumer advocates.

Although only a week from a vote on the plan, negotiations are continuing that could reshape the scheme.

A spokesman for Calpine Energy, which owns Westbrook Energy and two other large Maine plants that turn natural gas into electricity, said the company is concerned it may not get any credit for operating what are already clean and efficient plants.

John Flumerfelt said the company objects to a provision that would allow the state to keep some of the carbon dioxide allowances and sell them to the power plants to raise money for energy-efficiency programs or ratepayer rebates.