'American Idol' Judges NOT A Done Deal -- and Mariah Carey is PISSED

Nicki Minaj may well become a judge on "American Idol," but it will be at the expense of Mariah Carey, who we're told hung up the phone when she was told Nicki was the top candidate.

Sources connected with "Idol" tell TMZ ... Mariah was led to believe she would be the only woman on the judge's panel. Choosing Nicki would not only crush that expectation, it would add insult to injury because Nicki (29) is a lot younger than Mariah (42).

As for the composition of the judge's panel, we're told by no means is it a done deal. There are 2 scenarios being played out. First, it's unclear if Randy Jackson will come back as a judge or a mentor. If he leaves the judge's panel, there will be another spot to fill.

The second scenario ... we're told some of the honchos believe it's a mistake to have 2 women and a man on the panel, and a 4th male judge would be necessary.

As for who's still in the running, we're told Brad Paisley, Keith Urban and Enrique Iglesias are leading the pack.