Attempts to tackle global warming are being made more difficult by the spreading economic crisis even as Democratic congressional leaders say it's still a top goal for next year.

At the very least, fear of a prolonged economic downturn is expected to delay attempts by the United States to cap greenhouse gases blamed for global warming.

Democratic leaders in the House and the Senate as well as both presidential candidates say addressing climate change by imposing mandatory restrictions on heat-trapping pollution — especially carbon dioxide from burning fossil fuels — remains a priority.

Only months ago, the prospect of climate legislation passing in the next Congress and becoming law looked promising. Both presidential candidates Barack Obama and John McCain support mandatory emission cuts and a Democratic majority vowed to act on the problem early in the new year.

But the most popular remedy for slowing global warming, a mechanism known as cap-and-trade, could put further stress on a teetering economy by raising energy prices.

Democrats in both the House and Senate have unveiled draft climate bills. But their supporters acknowledge that the bills may have to be changed, given the economic situation. For example, a proposal to auction off emission permits — a source of money to help refocus the nation's use of energy away from fossil fuels — may have to be abandoned with permits distributed for free.

But some Republicans argue the whole idea of a climate bill ought to be scrapped for the time being. Limits of carbon dioxide would increase energy costs and lead the country "off the economic cliff," said Rep. Joe Barton, R-Texas.