Maine is joining six other Northeastern states in an initiative to reduce greenhouse gas emissions from the region’s power plants by 10 percent.

In what is being billed as the first regional compact of its kind in the U.S., the seven states will cap carbon dioxide emissions at the current level beginning in 2009 and then require incremental reductions of the greenhouse gas through 2019.

While supporters predict the accord will eventually lead to lower utility bills, they also acknowledge that energy costs will likely rise slightly during the program’s initial years.

Gov. John Baldacci joined with the governors of New Hampshire, Connecticut, Vermont, New York, New Jersey and Delaware in announcing the accord, which has been dubbed the Regional Greenhouse Gas Initiative, or RGGI.

“Maine is leading by example to protect our energy and environmental resources, and RGGI is another crucial step,” Baldacci, who has focused on reducing greenhouse gas emissions throughout his term, said in a statement.

The program would use what’s known as a “cap-and-trade” approach to reduce carbon dioxide emissions in each of the participating states.

Each state will cap emission levels beginning in 2009. In Maine’s case, that cap has been set at 5.9 million short tons of carbon dioxide.

Power plants will then be required to reduce their emission levels. Companies that achieve higher-than-expected reductions can bank them or sell those allowances to other companies struggling to meet their objectives.

Power plants will also be able to offset some of their carbon dioxide emissions by reducing emissions of other greenhouse gases, such as methane and other landfill gases, in other operations.

This “cap-and-trade” approach is regarded as more flexible and encourages companies to go beyond the stated reduction levels. The initiative is also notable because it sends a signal that states are willing to set concrete reduction levels for greenhouse gases – something the Bush Administration has steadfastly opposed.

“The federal government is not acting on this, so the states need to band together to act on this, and that’s what’s happening,” said David Littell, deputy commissioner of the Maine Department of Environmental Protection.

An analysis conducted for RGGI supporters estimated that households could see their electricity bills rise by $3 to $16 annually, although some industry representatives said they believe those figures are low.

John Flumerfelt, the Boston regional spokesman for power generator Calpine, said he does not expect that rates in Maine will be seriously affected by the initiative.

Flumerfelt also said Maine is well-positioned already because it has among the highest proportion of clean-burning power plants. Calpine’s three natural gas plants in Maine already use the latest pollution control technology, he said.

Overall, Calpine was “generally supportive” of RGGI, he said.

“No one would claim it’s a perfect package, but it’s a political compromise between the seven states,” he said.

Tuesday’s announcement followed a flurry of meetings among the states in recent weeks to hammer out a compromise. In the end, Massachusetts and Rhode Island elected to withdraw from the accord although they can still opt in.

Dave Wilby, executive director of the Independent Energy Producers of Maine, which represents power plants using renewable energy, said one positive result was that the RGGI process brought more attention to the issue of greenhouse gas emissions.

“I think those who have designed RGGI have really intended it to be a step toward and preparation for a national cap-and-trade system,” said Wilby, whose group did not have a formal position on the initiative.

The Maine DEP will now be charged with developing draft rules to implement the program.