Government assistance will be required if auto makers are to perfect plug-in hybrid vehicle technology, says Ford Motor Co.’s North American chief.

Speaking at a conference in Washington, Mark Fields says a government program to accelerate the development of PHEVs would help fast-track the technology.

“Tax breaks for hybrid technology proved to be an incentive of early adopters of hybrid vehicles leading to greater consumer acceptance,” Fields says. “In the same manner, incentives for plug-in hybrids will need support if they are to be developed for commercial viability.”

Ford isn’t the only auto maker to call on the U.S. government to provide assistance in the development of alternative powertrains.

In an April interview, Chrysler LLC Vice Chairman and former Toyota Motor Corp. board member Jim Press told BusinessWeek the Japanese government had subsidized “100% of the research and development costs” of the auto maker’s hybrid technology.

Toyota later disputed the claim, saying it received no assistance from the Japanese government.

Fields also says the U.S. is falling behind in the development of advanced lithium-ion batteries needed to power PHEVs.

“It’s also important to note most battery supply is currently being developed in Asia,” he says. “For those looking to plug-ins to answer our energy security concerns, we must ensure a domestic battery supply. Moving from imported oil to imported batteries clearly would not address this growing concern.”

Fields says “bold and dramatic” incentives are needed to accelerate the commercial development of high-energy batteries in the U.S.