WASHINGTON — Wooing independent voters, Republican Sen. John McCain called Monday for reductions in carbon emissions and criticized the Bush administration for failing to lead the fight against climate change.

"We have many advantages in the fight against global warming, but time is not one of them. ... We stand warned by serious and credible scientists across the world that time is short and the dangers are great," McCain said in a speech delivered at a wind-energy facility in Portland, Ore. "The most relevant question is whether our own government is equal to the challenge."

McCain, the presumptive Republican presidential nominee, proposed a "cap-and-trade" system to reduce greenhouse gases and allow the sale of rights to excess emissions by firms that reduce their own emissions. He also said he'd support auctioning off permits for excessive emissions, using the revenue to "help build the infrastructure of the post-carbon economy."

Such a system would "change the dynamic of our energy economy" by giving companies incentives to invest in alternative energy sources such as wind, solar, nuclear, clean-coal, biomass and biofuels, McCain said, providing the U.S. with an energy supply "that is safe, secure, diverse and domestic."

McCain set a goal of returning to 2005 levels of carbon emissions by 2012, and to 1990 levels by 2020, until the U.S. achieves at least a 60 percent reduction below 1990 levels by 2050.

McCain's proposal falls short of that of his Democratic rivals Hillary Clinton and Barack Obama. They both called for reducing emissions by 80 percent below 1990 levels by 2050, in line with what's recommended by most scientists, including the Intergovernmental Panel on Climate Change.