Fado, a traditional ballad style that is to Portugal what the blues is to the United States or the tango to Argentina, is a music of exquisite sadness. Although its origins are much in dispute, it seems to have emerged in Lisbon in the 19th century from a caldron of African, Brazilian, Arab and Jewish traditions. Sung originally in brothels and taverns, the lyrics -- often preexisting poems that are set to music -- mostly revolve around heartbreak, longing and the acceptance of one's destiny. (Fado translates as "fate.") The tone, relieved by the bright, metallic sound of the accompanying 12-string guitarra portuguesa, is soulful and dark.

It hardly seems a candidate for 21st-century global pop discovery.

But in the hands of singer Mariza Nunes, best known simply as Mariza, fado is also a music of subtle shadings and unexpected possibilities.

She's just 29, but her two albums, striking stage presence and dramatic performing style have already established her as a worthy successor to Amalia Rodrigues (1920-1999), the grande dame of fado. But Mariza doesn't seem content with re-creating the past. Musically, she has set herself on an ambitious path: honoring the tradition while updating it.

"Fado can take very long steps," she said in an interview in her dressing room before a concert in Miami a few weeks ago. "Obviously we have to respect tradition, but I grew up around fado and know it well, and if we don't start doing something to break barriers around this music, in 10 years we're going to go to a museum to hear someone talk about how there was once a music called fado."

She paused, then continued: "Culturally, this is a very important music, because the words we sing are poems by important poets. But at the same time we have to modernize fado."

On "Fado em Mim" ("Fado and Me"), her 2001 debut, she included both classics and fados. For her follow-up, this year's "Fado Curvo" ("Curved Fado"), she focused on new pieces. As for her sound, Mariza has stretched the standard classical guitar-and-guitarra portuguesa accompaniment to include cellos, pianos and trumpets. She has expanded the harmonic vocabulary and even shaded her vocal interpretation to hint at jazz (and check the muted trumpet in "O Deserto" in "Fado Curvo").

And hers is a revolution of visual style as well as musical substance. As part of a new generation of singers that includes Misia, Dulce Pontes and Cristina Branco, Mariza has been challenging the traditional image of stern-looking fadistas shrouded in black mantillas, and clearly having fun with it.

Model-thin and petite (she seems taller onstage), she keeps her short, bottle-platinum-blond hair coiffed in tight waves. The exotic features of her face hint at a complex genealogy -- born in Mozambique of a Portuguese father and an African mother and raised in Lisbon, she also claims Indian, German and Spanish blood.

Although in concert she holds on to the shawl as if to a link to fado's history, her look -- a mix of corseted dresses or long skirts, big jewelry and colored, striped socks -- is at once regal and funky. As she paces the stage, she at times seems to have stepped out of a Velazquez painting into an MTV video.

But a sense of fashion would have taken her only so far. Mariza has a powerful voice, impeccable intonation and a feel for the dramatic that often turn songs into breathtaking three-minute plays. (Perhaps not surprisingly, opera diva Maria Callas is her idol.) But when asked about being hailed as the successor to Rodrigues, her voice softens to a whisper and her tone turns reverential. (Not that she shies from such comparisons. On "Fado em Mim," she included several songs, "Maria Lisboa" and "Barco Negro" among them, commonly associated with Rodrigues.)

"Amalia was fantastic -- all around," she says. "Can you imagine a woman who starts out making a living selling oranges in the street . . . and has such a career?

"So when they compare me with the great diva, I feel it's fantastic but also unfair. Because when people talk about Amalia, they think of the 40-year-old Amalia, in her prime, and I'm not yet 30. I haven't lived enough."

Mariza grew up in Mouraria, an old neighborhood of Lisbon. Her father, once a civil servant in Mozambique, had returned home after the Portuguese colony gained its independence in 1975, essentially an immigrant in his own country. "He came back with a wife and a [3-year-old] girl," Mariza says, "and without a job, a home or any money."

The family opened a tavern -- Mariza's mother working as the cook, her father the waiter -- and acknowledging the strong fado tradition in the neighborhood, they instituted a Sunday afternoon fado session that became popular at a time when the musical style was otherwise at a low point.

Fado had become associated with dictator Antonio de Oliveira Salazar's regime, which fell in 1974, as part of what came to be known as "the three F's: Fado, football and Fatima," a sort of Portuguese version of "bread and circuses" involving entertainment, sports and religion.

"People didn't want anything to do with fado. It was seen as part of the regime. But the music was not to blame for it. It was manipulated," Mariza says, speaking in a whisper, switching back and forth between Spanish and Portuguese, sometimes in the course of a single phrase. "But in the '80s if you wanted to listen to fados you had to go to the neighborhoods, and you couldn't tell your friends because it was an embarrassment."

Mariza started singing fados as a child. The family's living quarters were over the restaurant, and her mother didn't want her to listen to the music.

"She said this was grown-ups' music and that I was too little," she recalls. But she watched and listened through an open door and can still remember "the dark room, the cigarette smoke and the sound of the Portuguese guitar, a sound that still today fascinates me. I knew then that I wanted to sing."

Her father looked for lyrics that might be appropriate for a child and taught them to her by drawing cartoons. "I didn't read yet," she says with a laugh. He also recorded the songs several times on a cassette, "and I'd go to sleep listening to the same song over and over. And that's how I learned them."

When she began to perform in clubs, she'd sing rock, bossa nova, funk and jazz -- and, now and then, at the end of the night, "if the mood was right," she'd sing a fado. "But I felt I was not a good fado singer," she says. "I felt I was too different."

As it turns out, the owner of a top Lisbon fado club heard her, invited her to take a weekly slot at his club, and a career as a fadista was born.

In a short time, this led to a television appearance at an Amalia Rodrigues tribute and Mariza's first recording, "because some of my friends insisted it was something I should do."

Recognition, at home and abroad, came at an astonishing pace. In 2000 she received the "Voice of Fado" award presented by Portugal's national radio station. By 2002 she was a hit at Womex, a world music trade fair, and at one point this year, her two albums were in the Top 5 in Portugal. In the United States, "Fado Curvo" hit No. 14 on the Billboard World Music chart in its first week and eventually reached No. 6.

Mariza progressed from playing a club in Lisbon to theaters and festivals throughout Europe, plus recent tours in the United States that included stops at the Hollywood Bowl and the Kennedy Center.

Even with all that success, "I don't call myself a fadista," she says with a playfully coy smile. "That's what the people in neighborhoods like Mouraria call you when they want to pay you a compliment. 'Ay fadista!' " she shouts, then drops back to a whisper. "I'm not there yet. I just call myself a cantadora, a singer. I still have to suffer a lot more to be a fadista."

Mariza is scheduled to appear tomorrow night at the Birchmere. To hear a free Sound Bite from "Fado Curvo," call Post-Haste at 202-334-9000 and press 8176.