The Obama Admin. takes another step towards regulating tailpipe emissions today with the Environmental Protection Agency determining greenhouse gases contribute to harmful pollution.

“This finding confirms that greenhouse-gas pollution is a serious problem now and for future generations,” EPA Administrator Lisa P. Jackson says in a statement accompanying the agency’s findings.

Earlier this year, President Obama directed the EPA to revisit a waiver request to the Clean Air Act filed by California last year but rejected by the Bush Admin., which cited a list of reasons why greenhouse-gas emissions should not be regulated.

Auto makers traditionally have opposed the waiver and battled California in the courts for years over what the state considers its right to regulate emissions for vehicles and other large producers of greenhouse gases.

The next step for the EPA is to post its findings for a 60-day period of public comment. It will hold hearings on the issue in Arlington, VA, on May 18 and in Seattle on May 21.

Auto makers have said granting the waiver would lead to a costly, state-by-state patchwork of regulations, but their stance has softened in recent months due to the economic crisis.

Nonetheless, the industry remains adamant emissions should be regulated by a single standard, either by existing corporate average fuel economy rules or a limit on carbon-dioxide emissions, a key greenhouse gas.

The determination by former EPA Administrator Stephen Johnson last year ran counter to a Supreme Court decision in 2007, which ruled greenhouse gases are air pollutants covered by the Clean Air Act.

The court said the EPA should decide if greenhouse-gas emissions from automobiles are a health threat, but Johnson argued his team could not determine if it represented a danger and essentially punted the controversial issue to the new administration.

More than 13 states want to regulate greenhouse gases under the same waiver requested by California.