Michael Jackson's sexual assault accusers Wade Robson and James Safechuck want a fortune ... MJ's estate says they're seeking $400 million in damages over the alleged abuse.

In new court documents -- obtained by TMZ -- MJ’s estate reveals the eye-popping figure in documents about a dispute with Paris Jackson over payment of their attorneys' fees.

Up until this point, no one knew how much Robson and Safechuck were gunning for ... as they continue their lawsuits against Jackson's companies, MJJ Productions and MJJ Ventures.

The estate says it’s buried in paperwork -- currently tied up in at least five litigations and arbitrations. As for Paris ... she’s fighting with the Estate's lawyers over mounting fees after they hired multiple law firms to handle various matters -- including the legal fight against Safechuck and Robson.

The Estate says if the lawyers aren't paid, it could be devastating … possibly forcing them to default in Robson and Safechuck’s lawsuit.

As we’ve reported … Robson and Safechuck both claim they were sexually abused by Michael Jackson as children, and detailed their allegations in the HBO doc “Leaving Neverland.” MJ was never convicted of any crime, and his companies continue to deny the allegations.

Us Weekly broke the story.