Chris Brown -- D.C. Prosecutors are Railroading Me!

Chris Brown says prosecutors in his Washington D.C. assault case screwed him over by unlawfully getting a sneak peek of witnesses ... so he wants the charges thrown out.

Brown's lawyer, Mark Geragos, says prosecutors had no right to take Brown's case before the grand jury. He says in his legal docs the U.S. Attorney had already decided to reduce the charge from a felony to a misdemeanor assault.

Geragos alleges the ONLY reason a grand jury was convened was to get a preview of how the witnesses in their case would fare under oath. In other words, Geragos says prosecutors used the grand jury for a dry run, and that's absolutely an egregious abuse of power.

A judge has yet to rule.