O.J. Simpson's Heisman -- Man Charged with Stashing Trophy ... For 20 Years

The man who allegedly tried to SELL O.J. Simpson's stolen Heisman Trophy and plaque has been charged in the case ... and faces up to 6 years in state prison if convicted ... TMZ Sports has learned.

As we previously reported, the suspect is ADAMANT he's not the person who originally stole the 1968 trophy and plaque from Heritage Hall at USC in 1994 ... but admitted he did barter for them in 1996, trading a Honda Accord and $500 cash.

Cops say the man hid the items for nearly 2 decades -- until late last year, when he allegedly tried to sell them -- heating up a case that had gone ice cold. Officials say the man knew the trophy was stolen when he came into possession of it.

The suspect was arrested Monday after nearly a year-long investigation ... and he was charged with one count of receiving stolen property. He's set to be arraigned later today.

As for the person who originally stole the trophy from USC -- still no lead on that person.