A clunky and difficult term to define for laymen and some politicians, "cap and trade" had become dirty words on Capitol Hill in recent months.

Republicans called the plan nothing more than "cap and tax" and one influential senator took great pains last week to declare cap and trade "dead."

Senator Joseph Lieberman, an independent trying to draft a bipartisan bill, said, "We don't use that term anymore."

Instead Lieberman said, laughing: "We will have pollution reduction targets."

But Lieberman did say it was still possible utilities may be subject to a cap and trade system. Senator Thomas Carper, who chairs a clean air panel in the Senate, told Reuters on Tuesday that cap and trade for utilities was the way to go.

Under cap and trade, or whatever it's called, Washington would impose steadily declining limits on carbon pollution that companies could emit, in the hopes of battling global warming. The pollution permits they would be required to hold would be traded in a regulated financial market.

A bill passed by the House of Representatives last year would impose an economy-wide cap and trade program. That bill has been stuck in the Senate since last year.

Since then, other ideas have been discussed for controlling carbon emissions, including a carbon tax, "cap and dividend" and even "cap and trade with training wheels," where an independent board would set a narrow price range for carbon for eight years to give markets experience in trading permits before going to a full-blown cap and trade