April 2 (Bloomberg) -- The Obama administration’s fuel- economy standards for cars and light trucks, which are less aggressive than targets proposed by former President George W. Bush, face a legal challenge from an environmental group.

The Center for Biological Diversity, an Arizona-based conservation group, said it sued today to strike down rules announced March 27 that require cars to average 30.2 miles per gallon for 2011 models, up from 27.5 mpg currently. Light trucks must average 24.1 miles per gallon, up from 23.5 mpg for 2010 models, under the rules.

Bush proposed, yet never issued, a 31.2 mpg standard for cars and 25 mpg for light trucks. The environmental group claims the 2011 requirements ignore the problem of greenhouse gas emissions and are illegal because federal energy policy law requires fuel economy standards to be set at the “maximum feasible level.”

“Reducing the proposed fuel economy standards is a step backwards from the clean energy future President Obama has promised,” Kassie Siegel, director of the Climate Law Institute at the Center for Biological Diversity, said in a statement.

The lawsuit was filed today in federal appeals court in San Francisco. Department of Transportation spokesman Bill Mosley said in an e-mail that the agency will review the complaint and had no further comment.

Global Warming

The appeals court in 2007 struck down Bush administration fuel mileage rules for light trucks and sport utility vehicles, saying the agency failed to analyze the effects of greenhouse gas emissions linked to global warming.

The March 27 rules were announced as General Motors Corp. and Chrysler LLC face possible bankruptcy. Car industry trade groups have said in court papers that adhering to stricter emissions rules will cost manufacturers billions of dollars.

The Environmental Protection Agency is considering allowing California and other states to establish auto-emissions requirements that are stricter than the federal government’s. The previous administration had turned down the state’s request to set their own standards.

The case is Center for Biological Diversity v. Department of Transportation, 9th U.S. Circuit Court of Appeals (San Francisco).

To contact the reporter on this story: Karen Gullo in San Francisco federal court at kgullo@bloomberg.net.

Last Updated: April 2, 2009 20:05 EDT