The Obama administration on Tuesday unveiled new clean air and fuel-economy standards for cars and trucks that include first-time federal limits for tailpipe emissions.

Under the proposal, the fleetwide Corporate Average Fuel Economy (CAFE) standard will rise to 35.5 miles per gallon by 2016, accelerating the timetable for federal standards set in a 2007 energy law (PL 110-140), which would have required that standard to be met by 2020. The current standard is 27.5 miles per gallon.

Vehicles would have to meet a combined average emission level of 250 grams of carbon dioxide per mile.

The regulations cover model years 2012 to 2016, meaning auto manufacturers will have to immediately reconfigure their product lines in order to comply with the federal requirements.

The proposal adopts standards California and other states have long sought to impose that curb greenhouse gas emissions from vehicles. It also demonstrates President Obama’s willingness to use his executive powers to address climate change and set a national benchmark that supercedes state clean-air regulations.

Experts speculated the timing was designed to prod the Senate into enacting a climate change bill this year, by reminding lawmakers of the White House’s power to impose regulations unilaterally.

It also appears to lay the groundwork for a more sweeping executive order expected in the coming weeks: a so-called “endangerment finding” that would trigger a requirement for the federal government to regulate greenhouse gas emissions under the Clean Air Act (PL 101-549) without new legislation.

“They are continuing to show every sign that they are aggressively pursuing regulation. This is a driver for legislation,” said Kevin Book, managing director of ClearView Energy Partners LLC, a strategy and consulting firm. “Today’s announcement matters more in the context of the endangerment finding. But it signals clearly that an endangerment finding is coming.”

Paul Bledsoe, director of strategy and communications for the National Commission on Energy Policy, which advised Congress on energy matters, said, “It’s another in a series of indications that this White House is serious about regulating greenhouse gas emissions. The legislative focus on healthcare has overshadowed the consistent determination of the president to get a handle on greenhouse gas emissions. It hasn’t gone away. This is an effort to remind everyone of that.”

Bledsoe said the regulations send a signal to the world that the United States is serious about climate change in advance of December negotiations in Copenhagen on a climate treaty to replace the expiring Kyoto protocol.

Obama in May announced a deal that ended a series of legal disputes over the California standards and set in place a program to establish nationwide regulations for fuel efficiency and greenhouse gas emissions.

“By bringing together a broad coalition of stakeholders — including an unprecedented partnership with American automakers — we have crafted a path forward that is a win-win for our health, our environment, and our economy,” EPA Administrator Lisa P. Jackson said at a White House news conference on Tuesday.

Transportation Secretary Ray LaHood predicted the standards would ensure consumer choice and save people money while reducing the nation’s reliance on foreign oil.