Diddy says the feds are trying to take him down purely because he's a successful Black man, and they're using a law that's been "racist" since its inception to do it ... according to new documents.

Diddy's attorneys filed docs Tuesday asking the judge to dismiss count 3 of the U.S. Attorney's case against him, which accuses him of "transportation to engage in prostitution" -- also known as the Mann Act.

It's been on the books as a federal statute since 1910, and Diddy points out it's the same thing the government used to take down rock 'n roll legend Chuck Berry and boxer Jack Johnson ... who were both -- not coincidentally, Diddy says -- Black men.

In the docs, Diddy says, "No other person, and certainly no white person, has ever been prosecuted under the White-Slave Traffic Act for hiring male escorts from another State."

As we've reported, the feds allege Diddy hired male sex workers to attend his so-called "freak off" parties -- but Diddy believes "he is being prosecuted for conduct that regularly goes unpunished."

Diddy's attorneys say prosecutors have built their case "based primarily on allegations that Mr. Combs and two of his longtime girlfriends sometimes brought a third party -- a male escort -- into their sexual relationship."

He goes so far as to say the hiring of escorts is "common and indeed widely accepted in American culture today." Diddy claims the escort service related to his case is a legit business operating "out in the open."

It's interesting ... Diddy's essentially copping to the crime, but accusing the government of only charging him because he's Black. According to the docs, his legal team believes the whole indictment is singling out Diddy due to race, but especially the Mann Act portion in count 3.

As for white people who've gotten away with this kinda thing ... Diddy holds up former NY Governor Eliot Spitzer, who was forced to resign in 2008 following his involvement in a escort scandal.