Legendary director Roman Polanski is once again being accused of "sexually predatory conduct" -- and the woman making the accusation is set to come forward today ... with a little help from Gloria Allred.



Allred and her mystery client are set to hold a press conference today in L.A. at 10:30 AM PST to explain the "legal significance of her allegations."

Polanski is currently under house arrest in Switzerland for that whole "skipping town before being sentenced for raping a 14-year-old back in 1977" thing.