In the absence of US laws regulating the gases that scientists link to global warming, the US Climate Action Partnership, a group of a 13 utility, energy, and insurance companies and four environmental groups, has laid out their vision of how to cut greenhouse gas emissions, setting a goal of reducing them by 60 to 80 percent by 2050.

US CAP was formed early this year by Alcoa Inc., BP America Inc., Caterpillar Inc., Duke Energy, DuPont Co., FPL Group, General Electric Co., PG&E Corp., PNM Resources Inc. and Lehman Brothers Holdings Inc..

Oil companies Shell and ConocoPhillips and insurance company AIG joined in recent weeks.

How the United States, the world's top emitter of greenhouse gases, will fight emissions is in focus ahead of the release on Friday of a United Nations report on how to tackle global warming.

US CAP favors a cap-and-trade market, first developed in the United States to reduce acid rain, to meet those targets.

In such markets, companies whose emissions levels rise over a set level can use allowances they received at the start of the program, or buy them from companies that cut emissions, to meet the limit.

The European Union, which launched the world's first greenhouse gas cap-and-trade market in 2005, gave away allocations to utilities, refineries, and heavy industry at the program's launch. Critics said that went too easy on emitters, kept prices and demand low, and did little to cut emissions.

Many critics of the US CAP plan say the group has opened a broader debate about how companies should cut emissions, but that the plan they are promoting could repeat Europe's mistakes.

They focus on US CAP's position that "a significant portion of allowances should be initially distributed free to capped entities."

Dave Hamilton, the head of climate programs at the Sierra Club, an environmental group that is not a member of US CAP, said, "We aren't wild about the free-at-first allocations."

The environmental groups in US CAP are Environmental Defense, the Natural Resources Defense Council, the Pew Center on Climate Change, and the World Resources Institute.

Hamilton said auctioning the allowances could put costs on emitters more quickly, and spur investment in technologies that could cut emissions, such as wind and solar power, and equipment that could bury carbon dioxide emissions from power plants underground.

An auction could, in effect, work like a carbon tax, which many economists say is the best way to regulate emissions because it puts costs on emitters that are more predictable than the volatile price of emissions that exist in a pure cap-and-trade market.

Even economists say a pure carbon tax may not be politically acceptable. But aspects of a tax could improve cap-and-trade programs, said Robert Shapiro, a former under secretary of the Commerce Department under former President Bill Clinton.

Since joining US CAP, power company FPL has come out in favor of an auction as well as a carbon fee on producers of coal, oil, and natural gas starting at US$10 a ton.

"There's not one absolutely perfect solution" to cut emissions, FPL spokeswoman Mary Lou Kromer said. The fee would spread carbon costs to all sectors of the economy, including vehicles, and not just focus on power plants, she added.

"There are fairly simple ways that a cap-and-trade can gain features of a tax system that are desirable," said Billy Pizer, an analyst at Resources for the Future, a Washington-based think tank.

No other US CAP members have come out publicly for a carbon fee, but the plan could evolve as Congress considers climate change legislation.