Diddy's firing back against claims of sexual misconduct ... filing a response in one of the many civil suits he's facing saying his alleged actions are time-barred -- 'cause the statute of limitations ran years ago.

The lawyers for the rap mogul, Bad Boy Entertainment and Daddy's House Recording fired off a letter in response to Crystal McKinney's sexual assault lawsuit ... saying the claims under the Victims of Gender-Motivated Violence Protection Law expired in 2010, seven years after McKinney claims Diddy assaulted her.

While her lawyers cited a local government ordinance that created a revival period for claims, Diddy's team says New York State Law takes precedence ... and state law says the time has come and gone for CM to make her claim.

The letter also argues that Bad Boy and Diddy's other companies can't be sued because they didn't facilitate the alleged misconduct ... so they can't be held liable for it.

ICYMI ... McKinney filed her suit back in May -- claiming she was invited to a Men's Fashion Week event at Cipriani Downtown in NYC where she says she met Diddy and he invited her back to his studio.

At the studio, Crystal says she drank Hennessy and smoked with Diddy and his crew ... and, felt like she was floating -- and, she claims the joint may have been laced.

She says Diddy then took her into the bathroom and forced her to perform oral sex on him ... after which she says she was blackballed from modeling -- leading to a suicide attempt the following year.

Diddy -- who was arrested Monday for sex trafficking -- has denied all claims of misconduct against him.