By John Crawley

WASHINGTON, March 4 (Reuters) - The Obama administration and automakers favor maintaining a single national standard for fuel efficiency, officials said on Wednesday as a bid by California to set its own requirement revs up.

Separately, Congress is close to setting a June 30 deadline for the Environmental Protection Agency (EPA) to decide whether California can proceed with its politically charged initiative that would improve efficiency by sharply reducing tailpipe emissions.

The provision is included in must-pass spending legislation now before the U.S. Senate. The House of Representatives has already acted on the measure.

President Barack Obama ordered the EPA in January to revisit the California matter after it was thwarted by the Bush administration in 2007.

The state must receive a waiver from federal law to proceed. A public hearing is scheduled for Thursday in Virginia.

The shared administration and industry position on a single standard provides important clarity ahead of the hearing with prominent industry interests and powerful environmental groups at odds over the best way to move forward.

It remains to be seen what approach will prevail nationally, if the Obama administration pursues the course it is leaning toward.

The California law, which is supported by a dozen other states, would require a 30 percent reduction in emissions by 2016. Burning less fuel or burning it more efficiently would improve gasoline mileage, experts say. The law, proponents say, is also designed to speed electric vehicles to market.