uring the mid-1970s, the landscape of American popular culture periodically witnessed something that in retrospect seems utterly implausible. Sitting in for Johnny Carson as host of "The Tonight Show," making chitchat with the various stars, starlets and other celebs of the day, was Beverly Sills.

Yes, an opera singer. In America's living room, behind that familiar desk in Burbank, disguised as a regular person -- which, let's face it, is what she was.

Sills, who died Monday at 78, achieved much during a long and varied career. She left behind the memories of many great performances, some (though not enough of them) documented on recordings. She helped reshape the cultural map of New York City through her leadership of the New York City Opera and Lincoln Center.

But her most distinctive achievement was at once simpler and more sweeping. By her very example, she got an entire nation to rethink what it meant to be a classical singer -- and by extension, what opera itself could mean in a nation where it was still an exotic cultural transplant.

There were plenty of American opera singers before Sills, of course, from Rosa Ponselle and Lawrence Tibbett to countless other stars of the major opera houses. But nearly all of them adopted the mannerisms and self-presentation
of their Old World counterparts.

The lesson was clear, and it's an idea whose remnants have still not fully died out: Opera is something that Europeans do. You can do it too, if you can pass for European.

It was left to Sills, with her plainspoken, folksy manner and unapologetic Brooklyn roots, to turn that truism on its head. Everything about her proclaimed proudly that yes, an artist could sing Donizetti and still be American to her very bones.

What Leonard Bernstein did for orchestra conductors, Sills did for opera singers. She showed that the supposed conflict between American populism and high art was in fact a false choice.

And that, in turn, had a profound effect on the way opera was perceived by people who might otherwise have regarded it with suspicion or indifference. The business of dressing up in costumes and telling an improbable story by singing it in a foreign language will always take a little salesmanship, especially in a country where the form is not a part of our native cultural heritage.

But Sills helped demystify opera for American audiences. In part through the very simple technique of showing up on television and being herself, she reclaimed it for what it truly is -- a branch of show business.

Sills' example has been lasting in some ways, but unfortunately not in others. American singers no longer have to look to Europe for their cues on how to behave in the world (though some, like Renée Fleming, do it anyway) or how to interpret the music they sing.

Along with Sills, singers like Marilyn Horne, Frederica von Stade and Samuel Ramey bring a distinctively American brand of energy and eloquence even to the standard works of the French, Italian and German repertoire. And a whole generation of younger artists,including singers such as Dawn Upshaw, Thomas Hampson, Susan Graham, Deborah Voigt and David Daniels, take that kind of approach practically for granted.

But at the same time, the popular perception of opera has backslid since Sills' heyday. The idea of opera among those who don't know it well has reverted to that old caricature of the foreign singer bestowing something exotic and sentimental on benighted audiences. The cause is obvious and summed up in three words: the Three Tenors. It was that regrettable marketing juggernaut, more than anything else in the past 20 years, that undid the good work of Sills and ther ilk.

What Sills had helped make plain and accessible, the Three Tenors made gaudy, incomprehensible and remote. To the public, their endless arena concerts and television spectacles said that America couldn't produce opera on its own after all, but had to import it from elsewhere.

In the actual opera houses of the United States and the rest of the world, of course, that canard is easily disproved. American singers -- intelligent, hardworking, impeccably trained -- are at the forefront of the international opera scene. But try telling that to the folks who are getting their impressions of that scene from the popular culture.

Today, a singer of Sills' caliber would face a daunting challenge just to get booked on "The Tonight Show" as a guest, let alone as a guest host. And it's not merely because our notions of celebrity have changed but also because the popular sense of what an opera singer looks and sounds like has changed. In the post-Three Tenors world, the likeliest operatic guest for Jay Leno would be the blind Italian tenor Andrea Bocelli -- the Vanilla Ice of opera singers.

Does it matter? Maybe not. The opera world continues to hum along nicely without much help from television talk shows, glossy magazines or the E! Channel. And in the end, Sills will be remembered far more for her artistic accomplishments than for anything she did on late-night TV.

Still, it's worth recalling a time when opera seemed so much more integrated into the cultural landscape -- less like the "irrational entertainment" described by Samuel Johnson and more like one form of art among many. And it's worth extolling the homespun, straightforward diva who helped make that possible.