By Deborah Zabarenko, Environment Correspondent

WASHINGTON, April 16 (Reuters) - President George W. Bush's plan to stop the growth of global warming emissions is bound to be part of his checkered environmental legacy, a record roundly criticized by conservation groups and political opponents.

The broad outlines of the plan call for letting U.S. carbon dioxide emissions peak in 2025, but offer no specifics on how to get there. Bush rejected new taxes, more trade barriers or abandoning nuclear power while focusing on emissions from the power industry.

With only nine more months in the White House, this kind of long-range plan from a lame-duck president found little favor with those already critical of Bush's stance on combating climate change.

"Unfortunately, President Bush retains the mantle of the most anti-environmental president in history," said Gene Karpinski, president of the League of Conservation Voters.

Karpinski noted Bush's promise during the 2000 presidential campaign to cap global warming pollution from power plants and said it was never honored.

"Since that time, all we've had is empty words but no serious action," Karpinski said by phone.

In the last two years, Bush has more publicly accepted the notion that human activities -- coal-fired power plants, fossil-fueled vehicles -- contribute to the problem and that the problem is serious.

But his administration has rejected economy-wide, mandatory programs to curb carbon dioxide emissions. This includes the carbon-capping Kyoto Protocol, which expires at the end of 2012.

A White House climate official left open the possibility for this kind of cap-and-trade program in the United States but others in the administration have dismissed current legislation before Congress that would set up such a program.

"The White House sees the handwriting on the wall and knows that regulations are coming one way or another ... What remains to be seen is whether the president is willing to support legislation that gets the job done," said Fred Krupp, president of Environmental Defense Fund. "On the details, he falls far short of the mark today."

If nothing is done to limit these emissions between now and 2025, energy-related U.S. carbon dioxide emissions are forecast to grow 12 percent from 2006 levels, the most recent year for which statistics are available, according to the U.S. Energy Department's forecasting arm, the Energy Information Administration.

The plan announced Wednesday will have no impact on Bush's legacy since it is consistent with the president's opposition to mandatory action to address the problem, said David Sandalow, a senior fellow at the Brookings Institution.

"We don't have voluntary speed limits in this country and voluntary limits on heat-trapping gases won't do the job either," Sandalow said in a telephone interview.

"His (Bush's) legacy overall will be viewed as a tragic failure to confront some of the most important challenges of our time with global warming at the top of the list," Sandalow said.

(Additional reporting by Tom Doggett; editing by David Wiessler)

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