US President Mr George W Bush has unveiled what he says is the largest raft of measures America has ever taken to safeguard the environment.
He promised to reduce greenhouse gas "intensity" by 18% over 10 years and other harmful emissions by up to 73% over 16 years.
Companies will be offered financial incentives to cut the amount of pollutants they put into the atmosphere.
By "greenhouse gas intensity", the president means the ratio of emissions to US gross domestic product growth.
Bush promised $4.6 billion over five years in tax incentives for the use of renewable energy and alternative fuels for cars. He said over two phases of eight years, sulphur dioxide emissions would be reduced by 73%, nitrogen oxide by 67% and mercury by 69%.
"This clean air legislation will constitute the most significant step America has ever taken to cut power plant emissions that contribute to health problems," he said.
The new environment policy has been condemned by Friends of the Earth as a "con-trick".
They say the plan seeks to confuse American voters by recommending greenhouse gas ceilings which sound like cuts but will actually allow further emissions growth.
Mr Bush has promised to cut greenhouse gas intensity by 18% over 10 years. But "intensity" means the ratio of emissions to US gross domestic product growth.
Friends of the Earth claim this target will not even require slower emissions growth. They say between 1990 and 2000, US greenhouse gas emissions increased by 14% while greenhouse gas intensity shrunk by 17.4%.