STEVENS POINT, Wis.    The Wisconsin wrestling squad opened its season at the UW-Stevens Point Open Saturday, placing twelve wrestlers in the top six and earning four championships.            Sophomores Tony Black and Justin Staebler, at the 125 lb. And heavyweight weight classes, respectively, both earned first-place finishes. NCAA qualifier, Grant Hoerr, at 141 lbs., and 2000 NCAA champion, Donny Pritzlaff, at 165 lbs., also took first place.    Sophomore Brad Owens at 133 lbs. and freshmen Nate Erdman and Ryan Lewis  at 149 and 165 lbs., respectively, earned second place finishes.  Finishing third at the tournament were sophomore Brad Marten, 174 lbs., freshman Ralph DeNisco, 184 lbs., and freshman Jareck Horton at 197 lbs.  Freshmen Tyler Laudon and Brady Reinke, 141 and 174 lbs., respectively, placed fourth.    The Badgers will next travel to Columbia, Mo., to compete at the Missouri Open on Sunday November 19, 2000.  Over 20 teams and approximately 400 wrestlers are expected to compete in the tournament.  Action will take place at the Hearnes Center fieldhouse on the University of Missouri campus.