As a longtime opera fan and a critic accustomed to examining the machinations of the opera world with a skeptical eye, I am surprised by very little. But I am flabbergasted by the decision of the Royal Opera at Covent Garden in London to drop the soprano Deborah Voigt from a new production of Strauss' "Ariadne auf Naxos" in June because she was deemed too heavy for a slinky black dress that is central to the director's concept of the role.

The company's move is so appalling that you have to wonder whether there is more to the story. Probably not. In a field where company managers and stage directors profess over and over that of course musical and vocal values come first, this action against Voigt offers distressing proof to the contrary.

The Royal Opera is not just replacing one of the leading dramatic sopranos of the day with a little-known German singer (Anne Schwanewilms). It is replacing the greatest living interpreter of this demanding Strauss role. Voigt first came to attention in a 1991 production of "Ariadne auf Naxos" with the Boston Lyric Opera.

I was there. Her triumph was total. The audience was awestruck. The next year she wowed Metropolitan Opera audiences with her performance of Chrysothemis in Strauss' "Elektra." James Levine, who was conducting, has made Voigt central to the Met's plans ever since.

The Royal Opera would seem to have forgotten the most basic truth of the genre. Yes, opera is a form of drama. But drama in opera has never been dependent on literal reality. Great music and great voices take you to the core of the drama and the essence of the characters. Naturally it's wonderful to hear fine opera singers who also look good and act well, and the new generation who grew up watching opera on television seems increasingly concerned with staying in shape and looking the part.

I remember being unexpectedly overcome by a student production of "La Boheme" at the New England Conservatory in Boston, sung in English and performed in an intimate theater. The endearing young cast clearly identified with Puccini's Parisian bohemians. They even looked a little tired and hungry, as haggard students often do.

But my first ever "La Boheme," a Met production that I attended as a teenager, starred Renata Tebaldi as Mimi. Tebaldi did not remotely resemble a consumptive and penniless seamstress. She looked like a pleasant, well-fed Italian lady. But her lustrous and poignantly beautiful singing was the embodiment of youthful desire, of sudden love coupled with a wariness of heartbreak.

Next week the Met introduces a new production of Strauss' "Salome" with Karita Mattila in the title role. Mattila, a strikingly lovely and slender woman, has apparently slimmed down even further for this role. Attractive as she is, Mattila will probably not resemble the adolescent Salome of the Bible. It won't matter, though. Opera creates its own kind of reality. What will matter is how well Mattila sings.

Commenting on the Royal's Opera's decision in a recent interview with The Sunday Telegraph in London, the company's casting director, Peter Katona, explained that its new Strauss production would forgo the typical setting. Instead of placing Ariadne on some stylized Greek isle dressed in a togalike costume, their Ariadne would be costumed in a sleek black modern dress.

But the character is not a Greek goddess. She is called the Prima Donna and is a typically temperamental soprano. She has been hired by the richest man in Vienna to sing the role of Ariadne in a serious new opera by an ambitious young composer as an entertainment for some dinner guests. In previous productions, Voigt has brought a wonderfully self-debunking comic touch to her portrayal. But after the prologue, when the opera of the "composer" is finally performed and the Prima Donna, playing Ariadne, begins the long soliloquy, Voigt fills those arching Straussian melodic lines with radiant outpourings of sound and effortlessly lifts them to the balconies. Suddenly the comic opera turns profound.

You can only feel for Schwanewilms, the soprano replacing Voigt. She is going to have to look pretty terrific in that dress to make London operagoers forget that they are not hearing Deborah Voigt.

This action also raises sobering administrative questions. The Royal Opera receives generous government support. Of course Voigt will be paid for performances she was contracted to sing. Does the Royal Opera have money to burn? How will it explain this move to patrons paying a top price of nearly $200 for prime seats?

Also, Voigt signed her contract nearly five years ago. When was the modern-dress concept arrived at? Is the company making this wrong-headed decision just to placate a director's last-minute whim?

Later this month, Voigt sings another of her signature roles, Sieglinde in Wagner's "Walkure" at the Met. Though Sieglinde is a demigod, the daughter of Wotan, she does not know this when we meet her. She is a sad and lowly young woman who has been forced into an abusive marriage with an oafish warrior. What should Sieglinde look like? Probably some slip of a thing. But in all of her past performances Voigt has been so vocally splendid and expressively honest that she becomes an affectingly believable Sieglinde.

Voigt said recently that she has again gone on a regimen of dieting and exercise. More power to her. But let her sing Sieglinde the way she always has, and Met fans will love her despite the size of her hips.