Capitol Police sources tell TMZ ... there's been a lot of chatter lately about officers tasked with guarding the Capitol come Wednesday and whether they're allowed to use deadly force if push comes to shove ... and if so, will they be backed by the Department?

Our sources say the issue came up at a roll call meeting last week, where one USCP officer asked his sergeants in the room, if they find themselves in a life or death situation -- like several cops did on Jan. 6 -- can they do whatever it takes to save their own lives, including the use of deadly force?

And, just as important ... would USCP brass have their backs in the aftermath? We're told the answer they got was NOT reassuring -- more of a wishy-washy response that catered more to optics and the need to accommodate peaceful protesters. In other words, the answer they got was vague and, many say, unhelpful.

There've been several suspensions, firings and resignations from the fallout Jan. 6. Some of the rank and file feel they've been made scapegoats ... and much of the discipline was unfair. All of this, we're told, has negatively affected morale.

It's not lost on the officers that they lost one of their own during the insurrection -- Brian Sicknick, who suffered a fatal injury. And, they heard the story of the officer who was dragged down Capitol steps and beaten. These cops want a clear policy on the right to use lethal force.