The movie star turned Republican politician said in a strongly worded statement that the Environmental Protection Agency's rejection of a request by California to be allowed to set its own standards was "legally indefensible."

The statement said California would file suit "within the next three weeks" at the District of Columbia Court of Appeals in Washington to challenge the EPA's ruling, which was issued on Wednesday.

"We will sue to overturn this ruling as quickly as possible," Schwarzenegger said. "I have no doubt that we will prevail because the law, science and the public's demand for leadership are on our side.

"Anything less than aggressive action is inexcusable."

"EPA's denial of our waiver request to enact the nation's cleanest standards for vehicle emissions is legally indefensible and another example of the failure to treat climate change with the seriousness it demands."

The EPA said on Wednesday that after consideration of the requests by California it had found there were no "compelling and extraordinary conditions" to grant a waiver.

The EPA instead said legislation signed by President George W. Bush this week was a step towards a "clear national solution" towards curbing greenhouse gas emissions rather than a "confusing patchwork of state rules."

Bush on Thursday echoed that view at a press conference in Washington.

"Is it more effective to let each state make a decision as to how to proceed in curbing greenhouse gases? Or is it more effective to have a national strategy?" Bush asked.

California passed legislation in 2002 requiring automakers to reduce vehicle emissions 30 percent by 2016. A total of 17 states had indicated they would adopt California's emissions levels.

However, for the law to take effect, California needed approval with a waiver from the EPA. Analysts say the Bush administration is opposed to California and other states setting their own standards because of fears of the effect it may have on the ailing US auto industry.

Although Schwarzenegger applauded the federal energy bill signed by Bush, he said it did not go far enough.

"The energy bill does not reflect a vision, beyond 2020, to address climate change, while California's vehicle greenhouse gas standards are part of a carefully designed, comprehensive program to fight climate change through 2050," he said in remarks on Wednesday.

Schwarzenegger has made the environment a key issue of his second term, signing a historic bill in September last year that saw the state become the first in the nation to impose limits on global warming gases.

Under the plan, California will aim to slash the state's carbon dioxide emissions by 25 percent by the year 2020, a figure that Schwarzenegger has said is equivalent to removing 6.5 million vehicles from the road.

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