"So today I challenge our nation to commit to producing 100 percent of our electricity from renewable energy and truly clean carbon-free sources within 10 years," he said.

Gore also took aim at the Bush administration's policies on climate change, without mentioning the president by name. Advocates of tougher measures to combat global warming caused by carbon emissions have long said President George W. Bush has done too little about climate change.

Gore, who faced a smattering of protesters rallying against big government outside the hall, likened the fight against climate change to the successful challenge in the 1960s to send humans to the Moon within the decade.

Gore, who starred in the Academy Award-winning documentary "An Inconvenient Truth" about the perils of global warming, also disparaged goals set too far in the future.

"A political promise to do something 40 years from now is universally ignored because everyone knows it's totally meaningless. Ten years is about the maximum time that we as a nation can hold a steady aim and hit our target."

Bush has opposed economy-wide limits on the emission of climate-warming carbon dioxide. Last week, he and other leaders of the Group of Eight major industrialized nations offered a non-binding pledge to cut emissions 50 percent by 2050 -- 42 years from now.

"WE MUST MOVE FIRST"

The Bush administration and the other rich nations said they could not meet this goal without participation from developing economies like China and India.

Gore, noting that an international climate change treaty is expected to be concluded by the end of the next US president's first year in office, questioned any delay on combating global warming.

"It is a great error to say that the United States must wait for others to join us in this matter," he said. "In fact, we must move first, because that is the key to getting others to follow; and because moving first is in our own national interest."

Democratic presidential candidate Barack Obama said he supported Gore's challenge, and said he would fast-track investments in renewable energy like solar, wind and biofuels if elected. "It's a strategy that will create millions of new jobs that pay well and cannot be outsourced, and one that will leave our children a world that is cleaner and safer," he said.

Obama's rival in the November election, Republican candidate John McCain, also backed Gore's plan. "If the vice president says it's do-able, I believe it's do-able," he told reporters.

Gore said he had had conversations with Obama, McCain, and with Bob Barr, the Libertarian Party candidate.

(Additional reporting by Thomas Ferraro, Editing by Frances Kerry)

(For more Reuters information on the environment, see http://blogs.reuters.com/environment/)