Not every singer lives to see her legacy formally presented while she’s still alive.

“Carnegie is calling it the Horne Legacy at Carnegie Hall,” says Marilyn Horne. “It’s a whole week devoted to the art of song. Master classes, seminars, individual coachings, talking sessions.” She adds, “It’s coming along really well.”

Horne, the American operatic mezzo-soprano, turned 80 last week. Her hair is white, her gait a tad unsteady, and she underwent treatment for pancreatic cancer in 2006 and 2007, but her build is still solid, her skin firm, her voice strong, her eyes twinkling, and her cancer gone. When she comes out on stage, she’s used to dominating it, even if her performance these days is devoted less to the operas of Rossini and more to singing the praises of her three grandchildren, Daisy, Henry and Alex. She’s delighted that the two younger ones have started playing instruments; she’s also a regular attendee of their soccer games. The only difference between her and the grandmother next door is that half of her anecdotes are being told to an audience from the stage of Carnegie’s Zankel Hall. What better place to celebrate a birthday?

In her prime, Horne was a star singer, singing with Pavarotti and Sutherland, Sills and Domingo, under the batons of Bernstein, Karajan and dozens more, in a huge cross-section of repertoire, from soprano roles at the start of her career to Marie in Alban Berg’s “Wozzeck” to her signature pants roles — in which a woman plays the part of a young man — in the florid and forgotten operas by Rossini and Handel that she made her own. That was enough to win her fame, national broadcasts, and, more recently, a host of career awards, from the National Endowment of the Arts Opera Honors to the Kennedy Center Honors.

But that alone might not get her an annual birthday party at Carnegie Hall — an event that’s so much a fixture that Samuel Ramey and Frederica von Stade, the two veteran singers who acted as emcees at the Horne celebration, were reprising roles they’d played often before, and even repeated (deliberately) a few things they’d said at her 75th.

Since Horne stopped singing, she has developed a flourishing second career as a teacher of young singers and a champion of art song. There are plenty of training programs for young opera singers, but fewer chances for them to cut their teeth in the song literature, and for 16 years the Marilyn Horne Foundation — launched at her 60th birthday gala — provided opportunities for young singers to give recitals around the country, singing everything from Schubert to Bolcom. Where opera has a certain populist streak, art songs are stereotyped as highbrow, and recitals are a hard sell; despite Horne’s energetic advocacy, she says, on some of those national tours, “there were times when there were 25 in the audience.”

The song, however, continues: In 2010, Carnegie Hall took over the organization, rechristened it with the “legacy” rubric, and has put its own considerable muscle into maintaining the event as a memorable opportunity for young singers. “Having Carnegie forces behind us is very different than the foundation,” Horne said appreciatively, speaking by phone from her New York apartment earlier this month. “We never had more than three people in [the] foundation, [in order] to stay in the black.”

It’s noteworthy that what Carnegie is calling Horne’s “legacy” is a product of this second act — not the operatic roles she did, or the accolades she received, but her work helping prepare subsequent generations of singers.

“Marilyn has done as much in the past 20 years with the young artists as she did in the 25 to 40 years before that as a singer,” says Matthew Epstein, the erstwhile manager and opera administrator who remains one of the field’s heavyweights, and a close personal friend of Horne’s.

No one would argue that Horne had significant influence as a singer — in part due to her choice of repertory. It’s less well remembered that she explored a huge range of music, starting out as a young singer in Los Angeles, when she hobnobbed with Stravinsky (whose “Oedipus Rex” was the vehicle of her La Scala debut in 1969) but also did the voice-over for Dorothy Dandridge in the film of “Carmen Jones.” But some of the works she championed, like Handel operas, have become opera-house staples to a degree no one could have imagined as late as 1984, when she got the Metropolitan Opera to put on “Rinaldo,” the first Handel opera the company had ever staged. Rossini was another, even greater, calling card. Maria Callas and Joan Sutherland are always named as agents of the “bel canto revival;” Horne is less seldom invoked, but was if anything an even more active bearer of the torch. Mezzos seldom get the credit they would like and may deserve.

“Though I’m at the top of my profession,” she wrote in her autobiography, “Marilyn Horne: My Life,” written with Jane Scovell and published near her 50th birthday, “I’m perpetually ‘on the brink’ of being a household word. You have to be a bit outrageous to be outstanding, particularly in the classical-music field.” Horne said she avoided doing things that seemed beneath her dignity. (This did not, evidently, include going on the Carol Burnett show with Eileen Farrell in 1968, dressed as the Three Little Pigs.)

The (sm)art song

The divide between highbrow and lowbrow, indeed, has played a defining role in Horne’s career all the way along.

“It’s an art form that exists to entertain,” says Horne, and she has the salty wit and down-to-earth approach to back it up. Singing alone, or with Joan Sutherland, or with Luciano Pavarotti, she could communicate a visceral thrill that’s hard to find these days.

Yet the part of her artistry she always seemed to want to emphasize was the more intellectual side: the art song, the exploration of unknown work. Opera, perhaps more than any other art form, calls on its proponents to be at once high artists and entertainers, and if the high art side of the picture gets more and more emphasis these days, Horne is playing a role in that as well.

In some of her performances, she seemed to downplay the visceral in favor of the polished technique, wielding a shining vocal instrument with adroitness and care. Witness, for example, the video of her 1981 Lincoln Center concert with Pavarotti and Sutherland, in which she stands between the others and powers out the word “No,” (singing a transposed bass role in the trio from Verdi’s “Ernani”) with the coolness of a jeweler displaying something precious — but without the character’s bitter anger.

“In its essentials,” wrote Peter G. Davis in the New York Times, “the concert could be heard as an old-fashioned glorification of the human voice, not so much as an instrument to achieve penetrating expressive ends but as a phenomenon to be wondered at for itself alone.”

And this sense of informed technique and vocal polish carries over to some degree into her teaching — and into her students’ performances. The singers at the birthday gala, including some of the notable names and rising stars in the field — Renee Fleming, Piotr Beczala, Brenda Rae, Jamie Barton, Isabel Leonard — offered perfect, almost airbrushed sounds, but seemed often to be constraining themselves emotionally. Barton, a mezzo with a beautiful pliant voice, showed a warm sound but cool diction in Mahler’s “Urlicht.” Leonard had one of the highlights of the evening with Monsalvatge’s lullaby to a black baby, sung with quiet conviction that brought the baby to life, but offered a disappointing climax with the showcase aria from Rossini’s “Cinderella,” one of Horne’s specialties, that was all showcase pyrotechnics, with no low notes and little substance beyond the shine. It evoked Davis’s description without conveying the same kind of excitement that Horne and her fellows used to generate.

Horne can frame some of the problems in terms of vocal technique. “Teachers are generally . . . teaching singers to sing more darkly,” she said. “I think this all has come to real fruition now. It all started way back with the microphone and television, and now HD [broadcasts] and electronic sound developed [so] now the darker singing sounds better, whereas the singing you really need, the good old chiaroscuro of Italian, is really on the back burner. There are fewer of us teaching that bright voice with darkness behind it, that’s got to carry. . . . I’m afraid we might be losing that great thrilling sound.”

But the issue isn’t technique alone; that’s the whole point. Watching the evening unroll, I wondered if Horne may be communicating to her students all the things that were most important to her, but not always getting across what made her great — perhaps because this is a kind of thing that’s hard to see about oneself.

At the end of the birthday gala, Barbara Cook took the stage for a final song, “Here’s to Life.” Cook, 86, was a partner in some of Horne’s relatively infrequent forays onto non-classical terrain over the years. Her voice in its current estate may not meet the standards of classical beauty. Instead, it has moved far beyond them. She sang about being old, and having lived fully, and yet wanting more; and she sang with such warmth and poignancy that tears prickled in many eyes. This is the meaning of singing. It’s something that Horne was, in many of her roles, able to access, along with the vitality, the brassiness and the round clear voice that helped made her a star. But it’s a difficult thing to pass on, and the Marilyn Horne Legacy — the official one — may not yet have found a way to include it.