Over the course of his Senate career, his score was a 24 percent, compared to lifetime scores of 87 percent for Clinton and 86 percent for Obama, both Democrats.

The Democratic candidates scored lower in 2007, with Sen. Clinton of New York scoring 73 percent for her votes and Sen. Obama of Illinois getting 67 percent, the report found.

McCain has sponsored legislation to combat climate change, and is described on his campaign Web site, www.johnmccain.com, as having a "record of common sense stewardship" of the environment.

However, he missed all 15 environmental votes for 2007 that were tallied in the report, including a vote on repealing billions of dollars in tax breaks for big oil companies, a measure that failed by one vote, the report said.

By contrast, Obama and Clinton each missed four of the 15 key votes on the environment last year, and both were on hand to vote for a version of an energy bill that would have repealed the oil companies' tax breaks.

"TURNING POINT"

Missing Capitol Hill votes is an occupational hazard of presidential candidates on the campaign trail, the report's authors noted.

The environment has rarely been seen as a pivotal election issue in the United States, but that may be changing, said Gene Karpinski, the league's president.

Pointing to results in congressional elections in 2006, Karpinski said independent voters moved in significant numbers to vote for Democrats, and "by far the single biggest reason was the issue of energy policy," which is closely linked to environmental policy.

"Clinton and Obama talk about global warming policy every day," Karpinski said at a briefing. "They've made this issue a priority because they know that's what voters want to hear."

The report noted an apparent shift along with the change from Republican to Democratic leadership after the 2006 elections.

"2007 may well be remembered as a turning point for the environment, and especially for clean energy and global warming," the report's overview said.

Following years of what the report called "backward-looking legislation" on the environment, the US Congress in 2007 passed the first increase in automobile fuel economy standards since 1975. This was part of an overall energy bill that also contains energy efficiency standards buildings and lightbulbs.

(Editing by Jackie Frank)