A Macheath for the 90's? Seated in the first row of the orchestra at the National Theater in Washington, a few blocks from the White House, John Dexter, the Tony Award-winning director of 'M. Butterfly' and 'Equus', is rehearsing Sting, Maureen McGovern and other cast members in Act I, Scene 2 of '3 Penny Opera'. It is Thursday afternoon Sept. 28, two weeks since the show, in town for a pre-Broadway run, was blasted by the local critics, who belittled Sting's acting ability, said his singing voice was barely audible and described the production as murky, boring and poorly directed...