OSLO, Norway — Environmentalists fete John Kerry as a possible savior in a stalled battle against global warming if the Democratic front-runner topples U.S. President George W. Bush in the November election.

"Kerry has probably been the greatest champion of climate change issues with (Joe) Lieberman in the U.S. Senate," said Jennifer Morgan, director of the WWF environmental group's climate change program.

European governments, among the strongest backers of the U.N.'s stalled 1997 Kyoto protocol meant to limit global warming, would welcome a shift towards Kerry's environmental policies after years of trans-Atlantic feuds with Bush.

"Clearly we would like the new administration, whether Republican or Democrat, to come closer to European policies on the environment in particular," said Diego de Ojeda, a spokesman for the European Union's executive Commission in Brussels. "It's better late than never," he said.

Bush stunned the world in 2001 by pulling the United States — the globe's biggest polluter — out of Kyoto, arguing the plan was too costly and wrongly excluded developing nations.

Massachusetts senator Kerry, who has won 15 of 17 Democratic primary contests so far, has berated Bush for ditching Kyoto rather than seeking to renegotiate.

Kerry now talks of taking part "in the development of an international climate change strategy to address global warming" — music to the ears of many Kyoto backers who view climate change as the biggest long-term threat to life on earth.

Kerry has also campaigned for green issues like better fuel efficiency in cars or against plans for Arctic oil drilling. By contrast, Bush did not use the word "environment" in his 2004 State of the Union address.

No Magic Wand

But a Kerry presidency would be no magic environmental wand. Kerry judged in 1997 that Kyoto would be unacceptable to the U.S. Senate and now reckons it is too late for Washington to sign up for the first round of cuts under Kyoto, in 2008-12.

The protocol aims to curb emissions of gases like carbon dioxide (CO2) spewed by factories and cars and blamed by scientists for blanketing the planet and driving up temperatures, bringing more droughts, floods, or typhoons.

Even so, some experts say the rise of a credible Democratic challenger to Bush could nudge an undecided Russia towards ratifying Kyoto, which will collapse without Moscow's backing.

"The fact that the United States has decided to stay out has been cited by analysts as an important factor in the reticence by Russia," de Ojeda said. "If the U.S. administration changed its position it might have a positive effect."

Kyoto has been ratified by countries producing 44 percent of industrialized nations' emissions but will only enter into force if it reaches 55 percent. Without the U.S. stake of 36 percent, Russia has a casting vote with 17 percent.

"Russia looks very attentively at the opinion of the U.S. administration, saying if the U.S. won't do anything then we won't either," said Alexander Nikitin, a Russian environmentalist. "A change in the U.S. position could well cause a change in Russia's as well."

Steve Sawyer, climate policy director at Greenpeace, praised Kerry for policies stretching back to opposing oil drilling off New England in the 1980s. "It's probably true that it's too late for the United States" to sign up for Kyoto, he said.

A surge in U.S. emissions since 1990 means that an abrupt shift from fossil fuels to meet Kyoto targets would threaten U.S. industries from coal fields in Montana to automakers in Detroit.

(Additional reporting by Oliver Bullough in Moscow, Patrick Chalmers in Kuala Lumpur)