The candidates had their first head-to-head exchange over the environment, a subject that has not figured prominently in their heated campaign, at their second televised debate at Washington University here.

The Republican Bush ticked off what he called several accomplishments of his administration, including measures to reduce pollution from off-road diesel engines, to increase wetlands, to clean the skies and protect forests.

"We've got a good, common-sense policy," he said, adding that he was counting on new technologies to improve the environment, including a hydrogen-powered car and clean-coal production.

"I guess you'd say I'm a good steward of the land. Quality of the air is cleaner since I've been the president," he said. "Fewer water complaints since I've been the president. More land being restored since I've been the president."

But Kerry retorted: "When it comes to the issue of the environment, this is one of the worst administrations in modern history."

He said the clean air initiative was doing more harm than good. "They're going backwards on the wetlands and water quality. They pulled back on global warming, declared it dead. Didn't accept the science.

"I'm going to be a president who believes in science," Kerry said.

Bush responded by defending his decision to reject the Kyoto treaty on climate change, saying the measure would have cost jobs. He said it was "one of these deals where, in order to be popular in the halls of Europe, you sign a treaty."

The president said he would press research and development. "That's the way to get from how we live today to being able to live a standard of living that we're accustomed to and being able to protect our environment better."

Kerry responded that the Kyoto treaty may have been flawed "but this president didn't try to fix it. He just declared it dead, ladies and gentlemen, and we walked away from the work of the 160 nations over 10 years."

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