Former President Bill Clinton on Monday praised Senator Barack Obama’s energy policy at the opening of the National Clean Energy Summit in Las Vegas.

But Mr. Clinton also lauded Mr. Obama’s rival, Senator John McCain, and said that either candidate would be progressive on the issue of climate change.

“Obviously, I favor Senator Obama’s energy positions, and Democrats have been by and large the more forward-leaning actors,” Mr. Clinton said. “But John McCain has the best record of any Republican running for president on the energy issue and on climate change.” He added, “I’m very encouraged about where the presidential rhetoric is in this campaign.”

Mr. Clinton’s remarks opened the two-day summit, held at the University of Nevada, Las Vegas, and organized by Senator Harry Reid, Democrat of Nevada, and John Podesta, Mr. Clinton’s former chief of staff.

Mr. Clinton challenged Nevada to tap its abundant wind and sunlight to become the first carbon-neutral state. He also questioned the recent rush to support offshore drilling.