PORTLAND, Maine — The Environmental Protection Agency’s declaration that carbon dioxide and other greenhouse gases are a public health danger is expected to have both short- and long-term effects on Maine, which already has begun regulating the gases on its own.

The action marks the first step toward requiring power plants, cars and trucks to reduce their release of pollution, especially carbon dioxide from the burning of fossil fuels.

“It’s a very important, historic decision for EPA,” said David Littell, commissioner of the Maine Department of Environmental Protection. “This is what Maine and other states have been saying EPA should do for years.”

The EPA’s declaration means Maine, California and other states should soon get clearance to enforce tailpipe emissions standards for new cars and trucks, Littell told the Portland Press Herald. The states adopted rules years ago that would effectively make new cars and trucks more fuel efficient, but the EPA has blocked the enforcement.

Maine also is part of a greenhouse gas cap-and-trade system that could serve as a national model. Anthony Buxton, a Portland lawyer who represents the Industrial Energy Consumer Group, said unless Congress acts carefully to come up with a way to regulate greenhouse gas emissions, it could be costly to industry and energy users.

“If we’re focused, we can do this right, and I think Maine is going to play a big role,” he said.

Under Maine’s system, the state has kept energy costs down by requiring that fees paid by industry go into energy efficiency efforts or back to customers.

“What we have to do now is exercise extreme vigilance and try to get Congress to emulate what Maine has done,” he said.