WASHINGTON, May 27 — Exxon Mobil has publicly softened its stance toward global warming over the last year, with a pledge of $10 million in annual donations for 10 years to Stanford University for climate research.

At the same time, the company, the world's largest oil and gas concern, has increased donations to Washington-based policy groups that, like Exxon itself, question the human role in global warming and argue that proposed government policies to limit carbon dioxide emissions associated with global warming are too heavy handed.

Exxon now gives more than $1 million a year to such organizations, which include the Competitive Enterprise Institute, Frontiers of Freedom, the George C. Marshall Institute, the American Council for Capital Formation Center for Policy Research and the American Legislative Exchange Council.

The organizations are modest in size but have been outspoken in the global warming debate. Exxon has become the single-largest corporate donor to some of the groups, accounting for more than 10 percent of their annual budgets. While a few of the groups say they also receive some money from other oil companies, it is only a small fraction of what they receive from Exxon Mobil.

"We want to support organizations that are trying to broaden the debate on an issue that is so important to all of us," said Tom Cirigliano, a spokesman for Exxon. "There is this whole issue that no one should question the science of global climate change that is ludicrous. That's the kind of dark-ages thinking that gets you in a lot of trouble." He also noted, "These are not single-agenda groups."

The organizations emphasize that while their views align with Exxon's, the company's money does not influence their policy conclusions. Indeed, the organizations say they have been sought out in part because of their credibility. "They've determined that we are effective at what we do," said George C. Landrith, president of Frontiers of Freedom, a conservative group that maintains that human activities are not responsible for global warming. He says Exxon essentially takes the attitude, "We like to make it possible to do more of that."

Frontiers of Freedom, which has about a $700,000 annual budget, received $230,000 from Exxon in 2002, up from $40,000 in 2001, according to Exxon documents. But Mr. Landrith said the growth was not as sharp as it appears because the money is actually spread over three years.

The increase corresponds with a rising level of public debate since the United States withdrew from the Kyoto Protocol, some of the groups said. After President Bush rejected the protocol, a treaty requiring nations to limit emissions of heat-trapping gases, many corporations shifted their attention to Washington, where the debate has centered on proposals for domestic curbs on the emissions.

"Firefighters' budgets go up when fires go up," said Fred L. Smith, the head of the Competitive Enterprise Institute. Myron Ebell, an analyst from the institute, spoke at last year's Exxon shareholders' meeting, where he criticized a renewable energy resolution proposed by a group of shareholders.

Exxon's backing of third-party groups is a marked contrast to its more public role in the Global Climate Coalition, an industry group formed in 1989 to challenge the science around global warming. The group eventually disbanded when oil and auto companies started to withdraw. As companies were left to walk their own path, Exxon shifted money toward independent policy groups.

"Now it's come down to a few of these groups to be the good foot soldiers of the corporate community on climate change," said Kert Davies, a research director for Greenpeace, which has tried to organize an international boycott of Exxon.

Exxon's publicly disclosed documents reveal that donations to many of these organizations increased by more than 50 percent from 2000 to 2002. And money to the American Legislative Exchange Council, a conservative group that works with state legislators, has almost tripled, as the policy debate has moved to the state level.

The gifts are minuscule compared with the $100 million, 10-year scientific grant to Stanford, which is establishing a research center that will focus on technologies that could provide energy without adding to greenhouse gases linked by scientists to global warming. Nevertheless, the donations in the tens of thousands or hundreds of thousands of dollars are significant for groups with budgets ranging from $700,000 to $4 million.

Critics say that Exxon and these groups continue to muddle the debate even as scientific consensus has emerged, and as much of the industry has taken a more conciliatory stance toward the reality of global warming. As Exxon has become isolated from its peers, it has faced increasing pressure from shareholders and environmentalists. BP, Shell and ChevronTexaco have developed strategies that incorporate renewable energy, carbon trading and emissions reductions.

Among the initiatives that Exxon's money has helped is the Center for Science and Public Policy. The two-month-old center is a one-man operation that brings scientists to Capitol Hill on two issues: global warming and the health effects of mercury.

"We don't lobby, we educate," said Bob Ferguson, head of the center, who spent 24 years working as a Republican Congressional staff member. "We try to be nonpolitical and nonpartisan and nonideological."