President Obama set specific greenhouse-gas emissions targets for the federal government Friday, saying it would aim to reduce its emissions by 28 percent by 2020.

The executive order, which covers 35 government agencies that must submit plans to the Office of Management and Budget by June for meeting the target, takes aim at the nation’s single-largest energy consumer, although it represents a small fraction of total U.S. energy spending.

The federal government spent more than $24.5 billion on electricity and fuel in 2008, Obama said, which is roughly 1.5 percent of the country’s total energy spending. According to Nancy Sutley, who chairs the White House Council on Environmental Quality, the government operates about 500,000 buildings and 600,000 vehicles.

“President Obama recognizes that it’s the federal government’s responsibility to lead by example in sustainability and on our efforts to build a clean-energy economy,” Sutley told reporters in a telephone news conference, adding that the plan aims to save $8 billion to $11 billion in energy costs through 2020. The 28 percent reduction will be compared with 2008 levels of emissions.

Sutley estimated that completion of the plan would amount to reducing greenhouse-gas emissions by 88 million metric tons by 2020 — equivalent to taking 17 million cars off the road for one year. The Office of Management and Budget will score each agency on annual performance toward meeting the goal and will release the score card to the public.