THE MAIN NOTES and themes of Peter Shaffer's "Amadeus" survive the Source Theater's overreaching "environmental" production, but the play itself is in essential disharmony with Source's limited resources.

"Amadeus" is an inventive, irreverent reconsideration of the legend that musical genius Wolfgang Amadeus Mozart was long thwarted and ultimately murdered by his jealous rival Antonio Salieri, court composer to the Austrian Emperor Joseph II. Transplanted from the Silver Spring Stage and starring Source founder Bart Whiteman as Salieri, director David Young's environmental concept calls for the audience to rise and move to a cramped corridor of the theater for a brief scene. It's a gratuitous but diverting gimmick, and the audience seemed to enjoy the novelty. And the exercise.

Source patrons are used to benevolently overlooking the inelegance of the troupe's necessarily modest sets and lighting. But in mounting "Amadeus," Source taxes every ounce of suspended disbelief in asking us to to imagine the action in the palatial digs of 18th- century Vienna. Perhaps a basement rec room in Vienna, Virginia. The halfhearted attempts at suggesting opulence -- some red velvet, dusty antiques and the gilding of the room's pockmarked columns -- only make it harder to swallow.

"Amadeus" gets by on some decent performances. Forever working his jaw and looking disgruntled and paranoid, Whiteman makes an amusing Salieri, "the patron saint of mediocrity," whose knowledge of his own limitations consumes him and his rival.

Iliff McMahan is a fittingly loony, nimble Mozart, and he convincingly produces "Wolfie's" infectious giggle on demand. And Elizabeth DuVall is luscious and worldly as Constanze, Mozart's bonbon of a wife.

The supporting cast fares less well. Norman Aronovic lays the dilettante emperor as Hermione Gingold, a silly touch that wears thin; the less said of his camp courtiers, the better. The players in the "spear-carrier" roles are allowed to draw too much attention to themselves, creating sour notes even before the show begins. Young has instructed the players to mingle with the crowd, performing parlor tricks and making small talk, an annoyingly superfluous role they are just not up to.