"I feel there will be a significant gap when it comes to whether they will really comply with the promises made during the presidential campaign," said Chief Cabinet Secretary Nobutaka Machimura, the government's number two and top spokesman.

Japan has tried to cast itself as a leader in the fight against climate change, which will be a key issue when the country hosts the summit of the Group of Eight major industrial nations in July.

Democratic candidates Barack Obama and Hillary Clinton have both vowed to tackle global warming, laying out detailed plans on how to cut US greenhouse gas emissions and cut dependence on foreign oil.

John McCain, the Republican Party's likely nominee, has clashed with more conservative members of his and President George W. Bush's party by declaring climate change to be a serious threat.

The United States is the only major industrial country to reject the Kyoto Protocol despite being the top emitter, saying the treaty is unfair by making no demands of fast-growing emerging economies such as China and India.

Despite the White House's stance, a growing number of local US governments have pledged action including those in California and New York City, which has launched a plan to cut greenhouse gas emissions by 30 percent by 2030.

Japan, despite its advocacy of the Kyoto Protocol named for its ancient capital, is far behind on meeting its own obligations under the treaty as its economy recovers from recession in the 1990s.

To the dismay of environmentalists, Japan allied with the United States at a UN conference in December in Bali to resist calls to set a clear numerical ambition for gas emission cuts between 2013 and 2020.

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