UNTIL 1972, IT WAS THE Redman. Now it's the Minuteman. Soon, it may be...well, who knows what's acceptable to the politically correct crowd these days? The University of Massachusetts at Amherst's armed white-male mascot has come under fire from students who deem the Revolutionary War soldier sexist, racist and militaristic. Chancellor David Scott initially agreed to hear the protesters out but changed his mind last week. "There will be no formal debate on the issue at this time," he announced. Meanwhile, exasperated alumni have been dialing campus officials to lobby for the Minuteman. Perhaps UMass sports fans will avoid the fate of spectators at ultra P.C. Stanford, who are subjected to football cheers led by a student dressed as a tree.