The two marked Earth Day by squaring off over conservation issues, which polls show have declined in importance with the American electorate in the last three years but still remain a weak point for Bush.

Bush traveled to a wetland area not far from his parents' estate in Kennebunkport, where he spent his vacations as a youth, and was greeted by some 200 protesters hoisting a poster "We're from Earth, you're from Mars."

The Republican sought to bolster his conservation credentials by announcing an "aggressive new goal" not only to protect existing marshlands harboring birds and other fauna, but add another 1.2 million hectares (three million acres).

Dressed in a casual jacket, the president defended his environmental record, saying, "We made tremendous progress during the last four years. ... My administration has put in place some of the most important anti-pollution policies in a decade."

Bush said his policies had reduced harmful emissions, reclaimed brown fields and cut the release of phosphorous material into US rivers and streams. "Since 2001, the condition of America's land, air and water has improved."

Kerry, who will face Bush in the November 2 election, traveled to Houston, Texas, to attend an Earth Day rally where he said the president had bowed to big business interests and compiled the worst environmental record of any US leader.

The Democratic senator said Bush had undermined enforcement of clean air laws, resisted controls on emissions of mercury and pulled the United States out of international agreements to deal with the problem of global warming.

"When it comes to the environment, George Bush has put polluters first," he said. "In three short years, one man and one administration have put the breaks on 30 years of environmental progress."

Kerry rejected the notion that economic development required environmental sacrifices. "I believe a strong economy goes hand-in-hand with a healthy environment, and when I am president, we will have both," he said.

Polls highlight declining support for Bush's handling of conservation. A Gallup survey conducted last month ahead of Earth Day showed only 41 percent thought the president was doing a good job on the issue, down 10 percent from three years ago.

The conservationist Sierra Club, a staunch critic, released on Thursday a new book for Earth Day titled: "Strategic Ignorance: Why the Bush Administration is Recklessly Destroying a Century of Environmental Progress."

"Bush has done his best, in only three years, to break our national compact on environmental progress and turn the clock back -- not years or decades, but a full century," said Sierra Club President Carl Pope, one of the authors.

John McCain, an influential Republican senator, urged Thursday resumption of discussions with European and other allies on ways to combat global warming, three years after Bush drew widespread criticism for pulling out of the Kyoto Protocol.

"We should be a lot more humble," McCain told the Council on Foreign Relations. "We should start opening negotiations on issues that are very important to our European friends."

But the surveys highlighted fading interest in the United States on environmental questions. Sixty-two percent of those interviewed in the Gallup poll said they worry a "great deal" or "fair amount" about the state of the planet, compared to 77 percent in March 2001.

Democrats tended to focus on the issue more, the polls showed. Forty-five percent said they worry "a great deal," as opposed to 18 percent of Republicans. Only 28 percent of Democrats rated the environment as "excellent" or "good," compared to 62 percent of Republicans.

TERRA.WIRE