Floria Tosca, the Italian opera diva and title figure in Giacomo Puccini’s opera “Tosca,” is one of the more challenging roles in the soprano repertory. She’s hotblooded, passionate, a little flighty, deeply loving. She commits murder for the man she loves, then plunges to her death when he, too, dies. All the while, she’s singing full throttle.

“I didn’t realize how much fun she was,” Patricia Racette says.

Clearly not everyone has the same idea of fun. But Racette, a 46-year-old American soprano in what she describes as “the meat of her career,” is having a ball.

Opera singers are stereotyped as being overblown, larger than life, divas; and the stereotyped reaction of people outside the opera world, on meeting them in person, is to realize how far many of them veer from the stereotype. Racette, sitting in her subterranean dressing room at the Kennedy Center, preparing for a rehearsal for the Washington National Opera’s production of “Tosca,” which will open the company’s season Saturday night, certainly doesn’t scream “diva” to a casual observer. Onstage, she can project a waiflike, vulnerable quality; off it, she’s down-to-earth, with a big, warm smile and a ready laugh sometimes punctuated by a yelp when something strikes her as particularly funny.

Racette hasn’t seized the limelight the way some of her American singer colleagues have done; in his rave review of her “Tosca” performances at the Metropolitan Opera in April 2010, the New York Times’ chief critic, Anthony Tommasini, called her “inexplicably underrated.” One reason she may be underrated is that she’s not a vocal powerhouse: singing, story-telling, dramatic effect are all equal parts of her artistic package. (Indeed, she’s shied away from recording: Sitting in a studio, without an audience, performing arias torn from their dramatic context, to her simply isn’t opera.)

Another reason is that she has performed such a wide range of music, from the lead in the world premiere of Tobias Picker’s “Emmeline” in Santa Fe, N.M., in 1996, to Gluck’s “Iphigenie” in Washington just a few months ago.

But it may be getting easier to pin her down. Her calendar these days shows a heavy focus on repertory staples such as “Tosca” and “Madama Butterfly.” She’s dreaming of “Manon Lescaut” — perhaps in Washington? — and looking, distantly, at some of the lighter German repertory.

“Early in my career, doing different repertoire turned me on,” she says. But, she adds, “what I really want to do in the meat of my career now is zero in on things that I can really do with great aplomb . . . where I feel like can offer both my best vocal and dramatic work, and . . . also offer something uniquely mine, artistically.”

“Tosca” is certainly a meat-of-the-career role; and a role that sopranos often wait, as Racette did, to tackle; the soprano brought it into her repertory only in the past couple of years, singing it in a staged production for the first time in 2010. Surprisingly, she found it completely congenial. In contrast with “Iphigenie,” which she says pushed her outside her comfort zone — the role sits relatively low in her voice, requiring her to hover in an upper-middle register that’s uncomfortable for a true soprano to stay in, without allowing her to move all the way up to the top — “Tosca” presented few challenges. “You can comment about what timbre you want to hear, or what weight voice you want in the role,” she says (her own soprano is a little lighter and more silvery than a full dramatic sound beloved of some old-school aficionados). But singing the part, for her, is “like taking a car on the highway■ It’s just the way my voice likes to function. There’s an intensity and a thrust in the singing that naturally happens.”

And though she’s wary of stereotypes, they emerge when she talks about playing an opera singer onstage. “It’s wonderful to portray a woman of strength,” she says. “What I love about the role is the truth of it, that uncontainable passion that she tries to get a hold of. . . . You know we [singers] wear our feelings on our sleeves. There’s no filter on us. When we try to control our feelings, it’s like a pot boiling with a lid.”

Racette embodies heart-on-the-sleeve with openness rather than manufactured drama, both on and off the stage. Indeed, she exudes a sense of comfort, even domesticity. Her latest project was the construction of a new home in Santa Fe with the mezzo-soprano Beth Clayton, her partner of many years whom she married in 2005. Clayton and their joint teacher, Trish McCaffery, are also artistic advisers who help keep her vocally balanced, and inform decisions about what roles, in the prime of her career, she wants to add to the mix.

“Beth has begged me to consider the Marschallin,” she says, referring to the lead in Strauss’s “Der Rosenkavalier,” who has an affair with a teenage boy, a role sung by a woman in pants that the 6-foot-tall Clayton would embody well. “We’d sell the lesbian community into the entire opera world,” she laughs. “But the role is so not me. I’m like, ‘Please don’t make me.’ ”