That debate will likely grow more heated following Exxon Mobil Corp.'s announcement last week that it is buying XTO Energy Inc. The deal will make Exxon, already a significant target of environmentalists, into the country's biggest natural-gas producer.
The industry has made the environmental benefits of gas a centerpiece of an $80 million lobbying effort that aims to promote increased use of gas to generate electricity and fuel cars and trucks. Burning natural gas releases about half as much carbon dioxide as burning coal to produce the same amount of energy and also emits far fewer smog-causing gases such as nitrogen oxide.
National groups such as the Sierra Club, the Environmental Defense Fund and the Natural Resources Defense Council have backed natural gas as a so-called bridge fuel that can help the country move away from coal and oil without waiting for renewable sources of energy, such as wind and solar power, to catch up.
The support of environmental groups has helped the industry win key backers in Congress, where a bipartisan "Congressional Natural Gas Caucus" formed this year.
But local opposition presents a challenge to the coalition. Grassroots groups have sprung up across the country to raise environmental concerns, particularly about the alleged risk of drinking-water contamination from hydraulic fracturing, a process in which large volumes of chemical-laced water are injected down wells to release gas trapped in underground rock formations.
Companies say that their drilling practices, including hydraulic fracturing, are safe, and that existing regulations are sufficient. There have been few independent studies to assess how widespread problems are.
"There are legitimate questions, and they can be answered legitimately," said Mr. McClendon, Chesapeake's CEO. "I feel we're on the right side of history here."
The pressure from local environmentalists appears to be having an impact. The Natural Resources Defense Council is now pushing for stricter regulation of drilling, the Environmental Defense Fund is working with companies to encourage them to adopt stronger environmental safeguards, and the Sierra Club has formed a task force to draft a policy on hydraulic fracturing.
James Marston, director of the Environmental Defense Fund's energy program, said the pros and cons of increased natural-gas use have turned out to be "more complicated than some of the early reports" indicated.
Concern appears to be growing in Congress, too, about the environmental impact of drilling. A House bill to regulate hydraulic fracturing has drawn 49 co-sponsors, and a companion bill has been introduced in the Senate.