Stevie J's aggressively defending his pal Diddy, and firing new shots at 50 Cent for his never-ending trolling over the federal raids and investigation ... something he thinks is racially-motivated.

We spoke to Stevie Tuesday on "TMZ Live," and he didn't hold back, accusing 50 of attempting to tear down the Black community ... so much so, he repeatedly labeled him an "Uncle Tom."

Stevie pointed fingers at 50 for spreading propaganda and lies about Diddy ... straight-up telling him to "stop being a girl and talking about him."

The longtime Bad Boy producer made it clear where his loyalty lies, and told us Diddy's in better spirits than you'd expect amid the ongoing federal probe.

Stevie says after 29 years of friendship, he can vouch for Diddy's true character.

He also shared his firsthand knowledge about the force federal agents used during the raids -- he was actually inside Diddy's Miami home when it all went down.

Stevie says the feds barged in, aimed weapons at him and ordered him outside with his hands up ... and then put him in handcuffs during the search. He says he saw agents leave with a single bag filled with potential evidence.

He said Diddy felt devastated the next day, especially because the feds removed his sons, Justin and King, from the L.A. home with guns to their heads.

For now, he says Diddy is focused on spending time with his daughters and mom.

As we've told you, Diddy has denied all the allegations made in several lawsuits, and Stevie says he will continue to have his friend's back.

He reminded Diddy's detractors, especially 50 Cent ... the man has not been arrested or charged with any crime, much less convicted of anything.