ABC's General Hospital, which won the Outstanding Soap Emmy, is offering further proof of its adeptness at tackling important social issues: Two popular characters, young lovers Robin and Stone (Kimberly McCullough and Michael Sutton), are faced with AIDS. The few other soaps to deal with HIV have copped out by giving the disease to characters to whom viewers were not emotionally attached. GH execs won't reveal the prognosis for Robin and Stone, but Sutton says, ''We're playing Romeo and Juliet for the '90s.'' And we know what happened to them. Still, the show promises a story that, as it plays out through November, will be more educational than downbeat. Executive producer Wendy Riche says, ''We're going to show the audience that knowledge [about AIDS] is power.''