SAN FRANCISCO - California has issues with federal attempts to weaken new vehicle pollution standards, but the state backed away on Wednesday from a report that it was threatening to pull out of a deal with U.S. President Barack Obama's administration.

The California agency responsible for implementing the state's global-warming law and vehicle-pollution standards said in a November letter that federal agencies must address two issues to ensure California's continued support for the national program.

California is fully committed to an agreement to harmonize state and federal rules, California Air Resources Board Chairman Mary Nichols said in a follow-up statement on Wednesday.

There are still difficult technical issues to be resolved, as is to be expected in developing any pioneering rule, but we are confident that they will be worked out successfully, she said.

California can set its own vehicle-emissions standards with federal approval and it received the go-ahead from the Obama administration last year. But when the federal government proposed a national plan by the Environmental Protection Agency and the National Highway Traffic Safety Administration based on the state one, California agreed to harmonize its rules.

The Detroit Free Press, which first reported the letter, had concluded that California may pull out of that agreement, which would create multiple markets -- and headaches -- for auto makers. That sparked the Wednesday statement by Nichols.

In the November letter, the state said it opposed an attempt to weaken proposed fuel economy standards for 2012-2015. The standards only go for one more year -- to 2016.

Further, the U.S. EPA needed to be less generous with credits to automakers, the letter said. The federal agency planned to call electric vehicles, plug-in hybrids and fuel cell cars 'zero-emission,' ignoring the pollution from sources providing electricity or hydrogen for the vehicle.

And overly generous credits for production of advanced vehicles might end delaying improvements on conventional vehicles, the California agency said.

A U.S. EPA representative did not immediately respond to a request for comment.

(Reporting by Peter Henderson; Editing by Gary Hill)

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