Few issues divide President Bush and Sen. John F. Kerry more starkly than the environment, where the two men have different approaches on matters ranging from curbing air pollution to promoting energy development on public lands. While Bush has focused on containing regulatory costs and has targeted selected issues, Kerry has advocated stricter federal rules on a wide array of fronts.

"It's hard to imagine another case where we've seen a more vivid contrast between the candidates than we see between George Bush and John Kerry on the environment," said Greg Wetstone, executive director of the Natural Resources Defense Council's Action Fund, an advocacy and lobbying group.

Bush took office without an extensive environmental record, but he has made his mark by reversing several Clinton administration initiatives, such as barring road-building and logging on nearly 60 million acres of public land and choosing to use market strategies to achieve environmental goals.

Environmental Protection Agency Administrator Mike Leavitt said the regulation-based approach the government used for years had worked on some environmental issues -- "the low-hanging fruit," in his words -- but that society has changed and federal officials are better off using market-based incentives.

"We have to use new approaches," Leavitt said. "We're not living in the same world, socially or economically."

The foremost example is Bush's hallmark Clear Skies initiative, which would create an emissions-credit-trading program to encourage power plant owners to reduce sulfur dioxide and nitrogen oxide emissions 70 percent by sometime after 2018. A separate initiative would mandate that power plants cut their mercury emissions by 70 percent within the same time frame.

Although energy industry officials embrace Leavitt's strategy, environmentalists say it undermines public health by failing to impose tougher limits sooner. Kerry sides with this camp and would add carbon dioxide to the list of controlled emissions because research has connected that pollutant to global warming. He has backed legislation that would cut emissions of four pollutants through a combination of pollution credit trading and mandatory reductions for every plant in the case of mercury.

On climate change, Bush has boosted funding for research but resisted calls for mandatory limits on greenhouse gas emissions. He has also opted out of the soon-to-be-enacted Kyoto climate change treaty on the ground that it would cost too many jobs.

Kerry, who has participated in virtually every major international climate negotiation, now says that it is too late to join Kyoto, which takes effect in 2008. He says he would restart international talks and push for legislation establishing a pollution-credit-trading system to cap domestic carbon dioxide emissions.

Bush's quest to produce energy on public lands puts him at odds with Kerry as well: For the past two years, Kerry helped lead the Senate fight against drilling in the Arctic National Wildlife Refuge, which the president supports. Bush has also approved about 70 percent more drilling permits on public lands during the first three years of his administration than Bill Clinton did during the preceding three years.

Sierra Club Executive Director Carl Pope said with this energy strategy, in addition to decisions to ease development on some wetlands and allow logging in national forests, the Bush administration had stripped environmental protections from tens of millions of acres of public land.

"Every president has left more of America's landscape protected than they inherited," Pope said. "Bush has gone in the opposite direction."

James L. Connaughton, who chairs the White House Council on Environmental Quality, called Pope's assertion "a fiction," saying that although a 2001 Supreme Court ruling left some wetlands open to development, the acreage involved is a fraction of the 20 million acres Pope estimated are now at risk.

Both Connaughton and William O'Keefe, president of the conservative George C. Marshall Institute, said Kerry takes extreme positions on environmental issues. O'Keefe said Kerry is "always pushing standards or goals without regard to costs or consequence," while Bush "tends to strike a balance between the benefits and costs and consequences of going forward."

But Daniel Esty, a senior EPA official under President George H.W. Bush who now directs the Yale University Center for Environmental Law and Policy, said, "This administration has walked away from environmental protection at the level that was advanced by presidents of both parties in the past."

Lynn Scarlett, assistant secretary of the interior for policy, management and budget, said the administration is focused on promoting "cooperative conservation programs," and has restored 1.7 million acres of wetlands and upland areas since 2001. "We want to build a nation of citizen-stewards instead of thinking all progress resides in Washington actions," Scarlett said.

League of Conservation Voters President Deb Callahan, whose group is backing Kerry, said Interior's conservation projects are "a nice little program, but it's a fig leaf in the context of the larger scheme of what we need to conserve in important public and private lands."