"These initiatives are a first step in what we expect to be an ongoing engagement with these and other sectors of our economy in the years ahead," President George W. Bush said in a statement.

The United States is the world's biggest emitter of greenhouse gases such as carbon dioxide, blamed by scientists for raising the Earth's temperature.

The White House refused to participate in the international Kyoto Treaty to reduce emissions, saying it would be too costly. Instead, the government opted for a program that encourages U.S. firms to set their own targets for carbon dioxide and decide if they meet them.

The Sierra Club, Environmental Defense and other green groups say a voluntary effort will do little to curb emissions. They back a Senate bill that would require steep cuts in carbon dioxide.

Energy Secretary Spencer Abraham said the voluntary program aims to reduce U.S. greenhouse gas "intensity" by 18 percent over the next decade. Intensity refers to the output of emissions compared to U.S. economic output.

Christine Whitman, head of the Environmental Protection Administration (EPA), said there would be no immediate reductions in carbon dioxide emissions.

"It's not going to get any smaller immediately, but we know that the overall impact is going to be over time and will get smaller," Whitman told reporters.

UTILITIES PLAN 3-5 PCT CUTS

Utilities including American Electric Power Co. Inc. (AEP.N), which runs the largest U.S. fleet of coal-fired plants, pledged to collectively cut their carbon output intensity by 3 to 5 percent by the end of 2010.

Utilities account for 40 percent of all carbon dioxide emissions, more than any other industry sector.

But a cut in intensity could actually mean that carbon dioxide emissions from utilities would increase by 16 percent over the period, said Jeremy Symons, an analyst with the National Wildlife Federation. That is because while utilities seek to reduce carbon dioxide output per unit of power generated, overall emissions would likely increase, Symons said.

On the electric front, the effort is headed by the Edison Electric Institute, whose 40 members include the largest U.S. utilities. The reduction targets are an aggregate for all members, and some utilities may come in above or below them.

A spokesman for Edison Electric Institute defended the targets as "fairly ambitious," and said the plan would slow carbon dioxide growth with the aim of eventually reversing it.

Oil refiners, another major source of carbon dioxide, set a goal of a 10 percent reduction in emission intensity by 2012.

Linn Draper, president of America Electric Power (AEP) and head of the Business Roundtable of the nation's largest 150 companies, said banks and other industries could also help reduce greenhouse gases.

Semiconductor manufacturers and mining, cement and aluminum makers are also taking part in the voluntary plan.

GIFT TO UTILITIES?

Environmental groups criticized the voluntary program as a gift to utilities from the Bush administration, which last year relaxed pollution limits on old, coal-burning power plants.

Carl Pope, director of the Sierra Club, said the program's focus on greenhouse gas intensity was a "shady accounting scheme" and that emissions would continue to rise.

Green groups and Senate Democrats back legislation reintroduced this week that would cut carbon dioxide emissions by 21 percent by 2009. The bill, offered by Sen. Jim Jeffords, a Vermont Independent, Democratic Sen. Joseph Lieberman and others, would impose the first limits on carbon dioxide.

The Bush administration has also proposed a plan to reduce emissions of other pollutants by 2018.