The Washington National Opera has replaced the three principal singers of its "La Traviata," but Wednesday night's performance made clear that the new cast met the challenge in this classic treatment of Giuseppe Verdi's beloved tragedy.

Andrea Rost (Violetta), Julian Gavin (Alfredo) and Vassily Gerello (making his company debut as Giorgio Germont) all matched the high standards established from the beginning of the run at the Kennedy Center's Opera House.

The toughest assignment was given to Rost, replacing Hei-Kyung Hong, whose performance had been transcendent. There were a few uneasy moments, right at the beginning, when Rost's intonation on a few notes was slightly unfocused, perhaps because of nervousness. But this passed quickly, and for the rest of the evening her singing was secure in the variety of vocal manners that the role entails, from the brilliant young hostess in the opening party scene to the despairing invalid on her deathbed in Act 3. The role of Violetta makes extraordinary acting demands, and she met them with a fine mixture of vulnerability and determination.

Gavin's light tenor voice can take on added power when needed. He uses it intelligently to characterize the impetuous, violent and belatedly repentant character of Alfredo, equally convincing in "De' miei bollenti spiriti" and "Parigi, o cara."

Gerello, who has been a member of the Mariinsky company in St. Petersburg, has one of the finest voices I have heard in the role of the elder Germont, and his phrasing and expression are as impressive as his tone. At times in Act 2, his body language showed signs of nervousness, whether from his unfamiliar surroundings or as part of his characterization of the role.

The three newcomers merged gracefully with the supporting cast (including members of the company's young-artist program and Placido Domingo's Operalia competition winners), which remained the same. Also unchanged are conductor Giovanni Reggioli's sensitive, skilled treatment of the score, the excellent response of the company's orchestra and chorus, and the lavish sets and costumes by Giovanni Agostinucci that add to this production's distinction.

Andrea Rost is secure in the challenging role of Violetta, and Julian Gavin is a convincing Alfredo in the Washington National Opera's "La Traviata."