Teresa & Joe Giudice -- Selling NJ House ... Before Heading Off To Big House

"Real Housewives of New Jersey" star Teresa and Joe Giudice are trying to make a quick buck before one or both of them go off to prison ... they've quietly listed their NJ mansion for $3.99M.

The couple -- who'll be sentenced next month for a massive money fraud scheme -- bought the place in 2002 for $530K ... then spent several years renovating it before moving into it in 2008 -- right when "RHONJ" was starting.

Originally, the house was around 5,000 sq. ft ... but after renovations, it doubled.

In 2012 it was worth about $1.2 mil ... they're trying to unload it for nearly 4 times that amount.

As we've reported ... Teresa faces 21 to 27 months in prison and Joe faces up to 46 months ... after pleading guilty to bankruptcy fraud and conspiracy to commit wire fraud.