Furious about the out-of-control MARIAH CAREYNICKI MINAJ bitch-a-thon raging backstage at “American Idol,” judge KEITH URBAN suddenly bellowed at the show’s producers: “This trash isn’t what I signed up for!”


He’s publicly playing it cool, telling interviewers everything’s ideal at “Idol,” but the Aussie country crooner’s crying the blues to execs and close pals – saying he wants to quit.


“They don’t pay me enough to have to deal with this crap,” kvetched Keith, who pockets a paltry $4 million a season, about half Minaj’s take – and chump change compared to diva Mariah’s whopping $18 million paycheck.


Insiders say Keith told execs: “I don’t want to be the peacemaker this entire season” – and he’d be grateful if they’d replace him.


“Keith knew there’d be friction between the two women, but had no idea how vicious and threatening it would become,” said a source.


"What makes him uncomfortable is the level the animosity has escalated to – and where it could go from here. And his wife, NICOLE KIDMAN, is concerned as well.”