California should take steps to reduce its greenhouse gas emissions 25 percent by 2020, Gov. Arnold Schwarzenegger (R) said yesterday, a move that would put his state in the forefront of international efforts to combat climate change.

While Schwarzenegger offered few details yesterday on his voluntary plan to cut carbon dioxide and other heat-trapping gas emissions, his announcement signaled the nation's most significant commitment to reducing greenhouse gases in years. The Bush administration has advocated more modest cuts in carbon dioxide emissions and has resisted imposing the kind of mandatory reductions most other industrial countries adopted in February as part of the Kyoto Protocol.

"Today I am establishing clear and ambitious targets to reduce greenhouse gas emissions in our state to protect our many natural resources, public health, agriculture and diverse landscape," Schwarzenegger said. He added that the state's Environmental Protection Agency secretary will lead a team to develop policies to achieve his goals.

Schwarzenegger's executive order, which he signed before a large and enthusiastic audience at San Francisco's City Hall at yesterday's opening of the five-day U.N. World Environment Day Conference, could reverberate across the nation because of California's size.

California has already adopted regulations to limit greenhouse gas emissions from automobiles, rules that several other states plan to implement in coming years. Several auto manufacturers, as well as the Bush administration, are challenging the new rules in court.

Under the governor's plan, California would cut its greenhouse gas emissions to 2000 levels in five years and to 1990 levels by 2020. By contrast, Kyoto calls for 141 nations to cut global heat-trapping gases by 5.2 percent below 1990 levels by 2012.

California's greatest cuts would take place over the next 45 years, at which point it would reduce emissions to 80 percent below current levels. That would match what atmospheric scientists have called for to stabilize the world's climate.

Thomas Graff, California regional director for the advocacy group Environmental Defense, equated the proposal to "this generation's 'man on the moon' commitment that inspires one of the world's top economies to take the lead in developing innovative solutions to our most serious environmental challenge, global climate change."

Bush administration officials emphasized that Schwarzenegger is not calling for mandatory greenhouse gas cuts. "We are pleased that like the president, Governor Schwarzenegger is apparently pursuing a technology- and incentive-based approach to meeting his goals," said James L. Connaughton, the president's top environmental adviser.