"The Bush administration is moving forward with a clear national solution not a confusing patchwork of state rules," EPA Administrator Stephen L. Johnson told reporters on a conference call. "I believe this is a better approach than if individual states were to act alone."
The long-awaited decision amounted to a serious setback for California and 16 other states seeking the new car regulations to achieve their anti-global warming goals.
The tailpipe standards California adopted in 2004 would have forced automakers to cut greenhouse gas emissions by 30 percent in new cars and light trucks by 2016, with the cutbacks beginning in the 2009 model year.
Under the Clean Air Act, the state needed a federal waiver to implement the rules.
"It is disappointing that the federal government is standing in our way and ignoring the will of tens of millions of people across the nation. We will continue to fight this battle," said Gov. Arnold Schwarzenegger. "California sued to compel the agency to act on our waiver, and now we will sue to overturn today's decision and allow Californians to protect our environment."
Twelve other states Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont and Washington have adopted the California emissions standards, and the governors of Arizona, Colorado, Florida and Utah have said they also plan to adopt them.
With Wednesday's denial, those other states are also prevented from moving forward.
In explaining his decision, Johnson cited energy legislation approved by Congress and signed into law Wednesday by President Bush. The law requires automakers to achieve an industrywide average fuel efficiency for cars, SUVs and small trucks of 35 miles per gallon by 2020 the first increase in the federal requirement in 32 years.
By 2016, California's law would require passenger cars and some small sport utility vehicles and trucks to reach 43.7 miles per gallon. Most pickups, SUVs and larger vehicles would need to achieve 26.9 mpg by 2016.
Johnson said Congress' approach of reaching a fleetwide average of 35 mpg would be better than a "partial state-by-state approach" that would achieve 33.8 mpg.
But environmental groups questioned Johnson's reasoning, noting that California's standards would be higher a full four years ahead of the congressional action and the federal 35 mpg was minimum requirement that future administrations could exceed.
"Mr. Johnson compared the California standard for 2016 with the new floor for the CAFE standard for 2020. This is fundamentally misleading," said David Doniger, director of the climate center for the Natural Resources Defense Council.
Wednesday's decision was further confirmation of the Bush administration's adamant opposition to mandatory limits on greenhouse gas emissions, even after a string of court decisions affirming the right of states and the federal government to regulate carbon dioxide and other greenhouse gases.
It was the first time the EPA had fully denied California a Clean Air Act waiver since Congress gave California the right to obtain such waivers in 1967.
California had been waiting for the decision for two years but EPA put off a decision while a Supreme Court case was pending on whether the agency could regulate greenhouse gases. In April of this year, the Supreme Court said it could.