By David Shepardson

WASHINGTON (Reuters) - The Obama administration proposed on Tuesday deeper government involvement in the design of autonomous vehicle systems and called on manufacturers to share more information about how such systems work and why they fail.

The wide-ranging proposal unveiled on Tuesday by the National Highway Traffic Safety Administration (NHTSA) called on automakers to voluntarily submit details of self-driving vehicle systems to regulators in a 15 point "safety assessment."

The plan came as automakers race to put autonomous driving systems on the road and regulators scramble to keep up. The emphasis on voluntary action reflected the reality, cited by regulators, that enacting formal rules could take years and securing congressional approval to expand NHTSA's authority faces political obstacles.

"This technology is moving so rapidly that it is outpacing the public policy that is necessary to make sure we're doing this properly," Senator Gary Peters, a Michigan Democrat, said Tuesday.

The proposals gave automakers and technology companies investing in automated driving many things they wanted, including a call for a single, national set of rules for self-driving cars. Throughout the document, titled, "Accelerating the Next Revolution In Roadway Safety," NHTSA cites the importance of fostering innovation.

U.S. Transportation Secretary Anthony Foxx said on Tuesday at a briefing for reporters the agency would seek to make it mandatory through the regulatory process.

"The industry now knows where we are headed," Foxx said, acknowledging that the policy leaves many questions unanswered now and will be updated at least annually.

A fatal crash in May involving a Tesla Motors Inc <TSLA.O> sedan highlighted the challenges for regulators. NHTSA had authority to ask Tesla for details of the system's design only after the crash.

"The absence of something like this policy creates a bit of a vacuum and makes it difficult for safety to be addressed properly," Foxx said.

Transportation officials said at a briefing they want Alphabet Inc's <GOOGL.O> Google unit, Uber Technologies Inc [UBER.UL], Tesla and others to answer safety assessment questions within six months about self-driving vehicles and systems such as Tesla's Autopilot, which allows limited hands-free driving on highways.

In what appeared to be a win for Google's self-driving car project, NHTSA said it could exempt up to a few thousand vehicles from regulations that require steering wheels and brake pedals for testing, but would need a change in law to permanently change the rules. Google has proposed fully autonomous vehicles without driver controls.

Uber is testing self-driving vehicles in Pittsburgh. Other automakers are testing their systems on public roads in other states.

The regulator said it wants to explore whether automakers should be required to submit technology to regulators for approval before they are offered for sale in a process similar to that used by the Federal Aviation Administration with aircraft.

NHTSA said it plans to propose a requirement that automakers report to regulators on the results of their testing of self-driving vehicle systems.

The next presidential administration and Congress will determine the future of NHTSA proposals.

Some consumer advocates called on NHTSA to go beyond voluntary guidelines and issue rules to govern autonomous vehicles before they are allowed on roads.

"This new policy comes with a lot of bark but not enough bite," Marta Tellado, president of Consumer Reports, said in a statement.

The NHTSA proposals touch an array of issues, from the ethics of robot-guided vehicles - should an automated car hit a pedestrian or protect the occupants of the vehicle in a case where a crash is unavoidable - to whether self-driving cars should be allowed to speed.

In that instance, NHTSA said self-driving cars should obey all traffic laws, including speed limits.

Industry groups on Tuesday praised the administration's call for federal standards for self-driving vehicles, instead of allowing states to set their own rules.

The NHTSA also urged states not to require a licensed driver for the most highly automated vehicles.

The California Department of Motor Vehicles, in a statement on Tuesday, said it "supports NHTSA's goal of creating a consistent approach and national framework" for self-driving cars.

The administration guidelines also call for sharing among manufacturers and regulators of data about problems encountered by self-driving vehicles.

IHS Markit analyst Jeremy Carlson said data sharing could be a sensitive issue. "There is a competitive aspect to all this data, all of the software," he said.

(Reporting by David Shepardson; Editing by Steve Orlofsky and Andrew Hay)