"This transition will not be easy, but it is crucial to begin now," the Pew Center said. "Further delay will only make the challenge before us more daunting and more costly."

The call for action came as a group of 85 evangelical leaders called on the US Congress to pass legislation that would require power plants, oil refineries, the transportation sector and other US industries to cut their greenhouse gas emissions.

The evangelical leaders, breaking with the White House, will roll out an advertising campaign; the group last year lobbied against gas-guzzling sport utility vehicles.

The European Union, Japan and most other industrialized nations are part of the Kyoto Protocol that imposes hard targets to reduce global warming emissions.

But President George W. Bush said the United States would not join the international agreement because it could hurt America's economy. Instead, his administration is promoting a voluntary program that US companies can join to cut their emissions.

The Pew Center said the administration must do more.

"The United States should declare its intention to work with other countries to strengthen the multilateral framework for climate action (and) the executive branch should analyze the full range of options and their potential consequences," the group said.

The report said the government must establish a "reliable and credible" system for tracking and reporting US greenhouse gas emissions.

A cap on emissions should be set for the whole US economy and then tradable allowances issued to emitters, such as large industrial sources and electricity generators, that each would represent the right to emit one tonne of greenhouse gases, the group said.

Low-emitting companies could then sell their allowances to companies that produced higher emissions.

The other steps recommended by the group include: converting fuel efficiency requirements for cars and trucks into average carbon dioxide emissions standards, boosting production of renewable fuels such as ethanol and biomass, and providing financial incentives to farmers to encourage the absorption of greenhouse gas emissions on agricultural and farm lands.