Joanna Krupa -- Not So Rich ... Faces Home Foreclosure

Joanna Krupa puts on a rich and famous front ... but TMZ has learned her home is on the chopping block because she owes a fortune in back mortgage.

A bank has filed foreclosure documents -- obtained by TMZ -- notifying her that her Encino home is going up for auction, because she's failed to pay nearly $725,000 she owes.

We don't know what it's worth, but it could be way upside down, because in 2004 the house sold for $670K.

The "Real Housewives of Miami" star is facing multiple problems, because the show is also on the chopping block. She's tried to jump ship to "Real Housewives of Beverly Hills" but we're told producers don't want her.

Too bad ... she could be the Andrea Zuckerman of the cast.