SAN FRANCISCO — California sued the federal Environmental Protection Agency on Wednesday, challenging its recent decision to block California rules curbing greenhouse-gas emissions from new cars and trucks.

Under the federal Clean Air Act, California has the right to set its own standards on air pollutants, but must receive a waiver from the E.P.A. to do so. The environmental agency broke with decades of precedent last month and denied California a waiver to move forward with its proposed limits on vehicular emissions of heat-trapping gases like carbon dioxide.

In a statement announcing the lawsuit, Gov. Arnold Schwarzenegger said, "It is unconscionable that the federal government is keeping California" from adopting new standards.

California officials argue that the agency had no legal or technical justification for blocking the new standards. The E.P.A. administrator, Stephen L. Johnson, said when announcing the decision that a new federal fuel-economy mandate would be more efficient in curbing pollution than the state standards.

The lawsuit also challenges the agency's contention that California is not uniquely affected by global warming and so lacks the "compelling and extraordinary" conditions that would allow it to regulate greenhouse-gas pollutants.

Mary D. Nichols, thechairwoman of the Air Resources Board, the state agency charged with putting California's 2002 law on vehicular emissions into practice, said the suit was filed quickly because "the states didn't want to sleep on their rights."

California regulators, Ms. Nichols added, have just calculated that in 2016, the state's standard would reduce carbon dioxide output by 17.2 million metric tons, more than double the 7.7 million metric tons that would be eliminated under the new federal fuel-economy standard.

California's cumulative reductions from 2009 through 2016 would be 58 million tons, she said — triple the reductions the federal standards would provide.