SINGULAR SENSATION New Yorkers have seldom been treated to Vesselina Kasarova’s complex voice and dramatic intensity.

Renée Fleming’s crème-caramel tones, the black-and-gold brocade of Dmitri Hvorostovsky’s timbre: Contrary to what some nostalgia buffs would have you believe, today’s operatic scene hardly lacks for great and distinctive voices. Among the most idiosyncratic belongs to mezzo-soprano Vesselina Kasarova, 41, who makes one of her infrequent local appearances on Tuesday 7, as Zayda in Opera Orchestra of New York’s performance of Donizetti’s Dom Sébastien.

The Bulgarian native’s repertoire runs the gamut from Monteverdi to Mahler, but she is most celebrated as an interpreter of the fierce and florid scores of Rossini, Bellini and Donizetti. Their so-called bel canto music showcases Kasarova’s agility and awe-inspiring variety of vocal colors—transparent gold and copper in her middle range, chocolate-brown down low, lightning flashes on high, all sheathed in a veil of smoke so luscious you can almost taste it.

“Her voice is very, very sensual,” remarks tenor Juan Diego Flórez, who sang opposite Kasarova in her 2002 Met debut in Rossini’s Barbiere di Siviglia. “It has a melancholic quality that brings so much humanity to her portrayals.” Kasarova’s Met career so far totals a mere nine performances of two operas—she has cancelled three other engagements—while OONY audiences have heard her in Rossini’s Tancredi (1997) and Bellini’s I Capuleti ed i Montecchi (1999).

Given the swagger and, well, ballsy quality of Kasarova’s singing as Bellini’s Romeo, the mezzo’s whispery, little-girl speaking voice comes as a shock. “I am a serious artist,” she says pleadingly by phone from Rome. “My Met cancellations were a coincidence.” She pauses. “I won’t just take cortisone and sing when I’m ill. I have too much respect for the public.”

Kasarova answered most questions by e-mail, claiming that her English and Italian were too poor for a real-time interview. Still, a quick chat revealed a woman who is articulate and firm in her views, for all her apparent vulnerability. “Vesselina is somehow shy, innocent, like a child, but she can be tough and clear when she has to be,” Flórez says of her. “That’s something you must have when you work in this world.”

Based in Switzerland, where she lives with her husband of 17 years and their young son, Kasarova sings a relatively limited number of dates each year. She has her sights set on vocal longevity, like her idols, Christa Ludwig and Giulietta Simionato. “They were intelligent—they had good techniques and long careers,” she says. Asked whether, like those legendary mezzos, she might be tempted to try out the odd soprano role, she replies immediately. “No, I’m happy with my repertoire. I have no problem playing the seconda donna. And there are few true mezzos today.…” Future years will see her take on Bizet’s Carmen, Nero in Monteverdi’s Incoronazione di Poppea and Edoardo in Rossini’s Matilde di Shabran. A Met return is under discussion for 2010 or later.

Along with her protean sound, Kasarova is also known for her highly individual manner of producing her tone—trills, for example, that can sound like someone gargling motor oil. When her voice took flight in a 2005 Cenerentola in Chicago, it was weightless and nimble, shimmering with tiny nuances of emotion; when it didn’t, she lunged her way through Rossini’s score. She shrugs off questions about mechanics: “I simply use the regular Italian technique—but I use it. Singing isn’t just reproducing notes in one and only one manner.”

She leaps, instead, at the chance to expound on her deeply serious portrayal in that work. “Many singers perform Angelina like Rosina in Barbiere di Siviglia, but if you study the score and libretto you see that there is absolutely nothing comic in her role. She has to master this difficult life, serving even the most evil people, in order to deserve to become queen.”

A crueler fate awaits Zayda, Kasarova’s OONY role: “True love can’t survive in a world dominated by the pursuit of power,” she says. “The woman becomes the victim in this fight.” From this unique artist who defines bel canto as “music that goes directly to the heart,” expect wild vocal thrills amid the tears.

Opera Orchestra of New York performs Dom Sébastien at Carnegie Hall Tuesday 7.