Two U.S. officials said that the Capitol Police will be asking for a 60-day extension of the National Guard and that it's being reviewed.
A third official said a formal request from the Capitol Police has not yet arrived at the Pentagon, though they are aware it is pending.
There are currently more than 5,000 National Guard members still in the city from a peak of 25,000 present for security at the Jan. 20 inauguration.
The scheduled end of the current mission for the remaining troops is March 12.
The need for the National Guard presence -- armed behind high fences topped with razor wire -- has become a focus of debate over how much security is needed around the Capitol going forward.
Michigan Democratic Rep. Elaine Slotkin put out a statement Thursday morning raising questions about how that's being determined.
"No one likes seeing the fortress-like security around the Capitol. And no one wants to again have a security problem in and around this symbolic place. But whether an extension has been requested or the mission is indeed terminating on March 12, it's critical that members of Congress get a briefing on what's behind these decisions," she said.
"We all have the same goal: to get back to the point where Capitol Police is capable of protecting us without the Guard's help, and all parties feel confident we can protect the people's business," she said.
Sen. Jim Inhofe of Oklahoma, the top Republican on the Armed Services Committee, blasted the request in a statement late Thursday.
"Keeping the Capitol Complex safe -- and open to the public, as it has been forever -- is a federal civilian law enforcement responsibility. We can and should make improvements to how the Capitol Police protect the building, and there are plenty of options available to us, such as changes to the U.S. Capitol Police force structure, availability of a non-military quick reaction force and mobile fencing," he said.
"What this solution should not look like is keeping the National Guardsmen here indefinitely, as has been rumored. This is not their job or their mission—and the image this would paint on the world stage is concerning," Inhofe added.
Asked about whether the National Guard needs to remain at the Capitol for two more months, House Speaker Nancy Pelosi said Thursday that "decisions about security are made by the security leadership here, and we'll see what that ask is."
"We should have them here as long as they are needed, and the silliness of this being Inauguration Day ... falls into the realm of let's not waste our time on it," she said. "We have to have what we need, and when we need it, and in the numbers we need it. But that's a security decision."
ABC News' Benjamin Siegel and Trish Turner contributed to this report.