WASHINGTON — As part of the climate change agenda he unveiled this year, President Obama made a commitment to significantly reduce the federal government’s dependence on fossil fuels. The government, he said in a speech in June at Georgetown University, “must lead by example.”

But just two miles from the White House stands the Capitol Power Plant, the largest single source of carbon emissions in the nation’s capital and a concrete example of the government’s inability to green its own turf.

The plant, which provides heating and cooling to the sprawling Capitol campus — 23 buildings that include the Library of Congress, the Supreme Court and Congressional office buildings, in addition to the Capitol building itself — is operated by Congress, and its transition to cleaner energy sources has been mired in national politics for years. But the failure of Congress to modernize its own facility also raises questions about the Obama administration’s ability to limit emissions from existing power plants when it has not been able to do so at a government-run facility so close to home.

The office of the architect of the Capitol, which oversees the operations of the plant, first moved to end the use of coal there in 2000 but was turned back by resistance from powerful coal-state senators who wanted to keep it as the primary fuel. The effort was revived in 2007 as a central part of the Green the Capitol Initiative, led by Nancy Pelosi, the House speaker at the time. The effort was defunded in 2011 after the Republicans took control of the House.