The timeline is part of Obama's plan to cut US oil imports by a third by 2025 and put a million advanced vehicles on the road by 2015.

"By December 31, 2015, all new light duty vehicles leased or purchased by agencies must be alternative fueled vehicles, such as hybrid or electric, compressed natural gas or biofuel," Obama said in a memorandum sent to heads of all US executive departments and agencies.

"The federal government operates the largest fleet of light duty vehicles in America. We owe a responsibility to American citizens to lead by example and contribute to meeting our national (energy) goals."

The memo updated a previous text dated October 5, 2009 in which Obama had asked that government agencies reduce their vehicle fleet's oil consumption by 30 percent.

At the time, the president was still counting on Congress to pass a bill fighting global warming, an initiative that ultimately failed in the face of opposition from lawmakers and that seems unlikely to return to the top of the Obama administration's agenda.

But Obama has continued to seek stricter pollution norms for light vehicles and trucks through regulation.

His latest memo also limits the size of the administration's vehicles and requires rigorous management of the fleet to correspond to needs. Emergency and security forces' vehicles are granted exceptions to the rule.

Copyright APP (Associated Press of Pakistan), 2011

Copyright AFP (Agence France-Presse), 2011