The Capitol Power Plant is one of the biggest contributors to greenhouse gas emissions in the District, a century-old building that spews a constant stream of carbon dioxide and other emissions into the atmosphere.

It’s the bane of environmentalists everywhere — and on March 2, more than a thousand plan to sit in front of the entrances and disrupt the plant’s operations.

“No one in D.C. you speak to supports the power plant. They think it’s dirty, it’s old,” said Matt Leonard of Greenpeace, who is helping organize the protest. “But the political will isn’t there.”

It’s mostly a symbolic gesture, environmentalists concede, one that is supposed to highlight their contention that the coal industry has a “stronghold” over the government.

The reason the power plant isn’t running completely off natural gas, they say, is opposition from two powerful Senators of coal-heavy states: Robert Byrd (D-W.Va.) and Mitch McConnell (R-Ky.). Capitol Climate Action — a coalition of more than 40 nonprofit groups and supporters such as Noam Chomsky — hopes the March protest will spread the message that such political obstruction is preventing environmental change.

Whether that’s true is hard to prove, though Byrd and McConnell have pushed for the power plant to use clean coal. On Tuesday, spokesmen for both Senators emphasized their support for using coal, while they avoided mentioning natural gas.

“Senator Byrd has been a supporter of the use of coal at the Capitol Hill power plant, but has also been an advocate of efforts to help ‘green’ the Capitol campus,” spokesman Jesse Jacobs wrote in an e-mail. An attempt to find ways to use carbon dioxide capture failed, he said, but “Senator Byrd will continue to explore other options.”

Senate leaders have also been noticeably quiet on the issue, despite Speaker Nancy Pelosi’s (D-Calif.) successful push in 2007 to switch a portion of the power plant to natural gas.

But there are obstacles beyond resistant Senators. The plant now uses 65 percent natural gas and 35 percent coal. For the plant to use 100 percent natural gas, the Architect of the Capitol would have to modernize a few boilers — at a cost of $7 million.

On Tuesday, Senate officials declined to give any indication of whether they will push for a cleaner power plant.

A spokeswoman for Majority Leader Harry Reid (D-Nev.) referred questions to the Senate Rules and Administration Committee, while a committee spokesman said no decision had been made yet.

Rules Chairman Charles Schumer (D-N.Y.) is waiting on an upcoming 10-year plan from the AOC’s office, said spokesman Brian Fallon.

“It makes sense to await the findings of that report before making decisions on how best to modernize and make cleaner the Capitol’s power generation facilities,” he said.

House officials, meanwhile, were happy to highlight their accomplishments on environmental matters, while declining to answer any questions on why the power plant isn’t running entirely off natural gas — or who has the authority to implement a change in policy.

So far, each chamber has focused on its own energy needs. As part of the Green the Capitol Initiative, Pelosi asked the AOC to purchase natural gas “to meet the heating needs of the House.” The Senate has stuck to replacing light bulbs, recycling and improved insulation.

Leonard hopes that changes on March 2 with calls from volunteers and hundreds of protesters practicing “civil disobedience.”

“For us, it’s less about that facility and more about the big picture,” he said, “but Congress needs to clean its backyard.”