What becomes a legend most, a famous fur ad used to ask. It’s a question on the minds of many these days, as a new century lives out its infancy and emerging technologies alter the way we perceive just about everything.

Of course, 100 years ago, before the age of celebrity as we know it, who would have predicted radio, television and the Internet, to say nothing of a moon landing? Yet both pundits and those involved in more practical trades find themselves wrestling with the question of who will join, or maybe even displace, the Bogarts, Mae Wests and Elvis Presleys that fill the niches we reserve for icons.

There are, of course, good commercial reasons for trying to identify these hot properties of the future, but there’s also pleasure in the sport of speculation. First, though, there must be a definition of terms. And agreeing on just what an icon is — and what an icon will be — isn’t so easy.

“It’s about being identifiable and original,” says Bernard Telsey, head of the powerful casting agency that bears his name. “Also, icons need to make a statement about the times they live in, and that will hold true for those who represent our era.”

For Tom Evered, general manager and senior VP of EMI Classics & Jazz, “An icon is somebody who’s been up and down, but when the floodwaters recede, they’re still standing.”

Kenneth Turan, the film critic of the Los Angeles Times, takes a page from Justice Potter Stewart’s book. “Being an icon is indefinable,” he says. “I really think it’s a you-know-it-when-you-see-it kind of thing, like the famous definition of pornography. We don’t need to be told who they are. It’s the cultural equivalent of falling in love.”

But people also fall out of love, according to Turan. “Take Lillian Russell,” he says. “She was an icon in her day, and now most people haven’t heard of her. I don’t know that the individuals we consider icons will be icons forever.”

Traditionally, the people we now consider iconic have come from the theater, radio, TV, popular music and, especially, movies. But that may not be the case in the future, especially as various barriers disappear. “I think people are looking everywhere,” says Turan. “It doesn’t really matter where they start; it matters how wide their reach ultimately goes. The starting point is almost irrelevant. The issue is how much they will break into the wider culture.”

As for who those people might be, the field is wide open. Michael Riedel, theater columnist at the New York Post, puts Nathan Lane, a generally popular pick, at the top of his list. He also suggests Hugh Jackman, but notes that “his movies haven’t really gone anywhere.”

Riedel’s also high on Bernadette Peters, as a musical star, and Cherry Jones, in the drama department. “If her name is attached to a play, you know it’s going to be quality, in the way that Helen Hayes in a play assured quality in the 1920s and 1930s,” he says of Jones. Glancing across the pond, he cites three great ladies of the English stage: Maggie Smith, Vanessa Redgrave and Judi Dench. “When they’ve shuffled off this mortal coil, they’ll be considered giants of their time, I’m sure,” he says.

Yet he doesn’t expect the theater in the 21st century to be the icon incubator it was in the 20th.

“Back when the Barrymores, the Lunts, Helen Hayes and even the Marx Brothers were around and even up through Ethel Merman and Mary Martin, theater was an integral part of the entertainment culture in this country,” Riedel says. “If you were a star on Broadway, you were a household name. But that shifted a long time ago. Stars today come from movies and TV. If you just have a career in the theater these days, chances are you’re not going to achieve iconic status.”

Turan, though, cautions against counting the theater out quite yet. “What hampers theater is its lack of reach,” he insists. “It’s the arts that have the widest reach that have the best chance of producing icons. I wouldn’t say it’s not possible in theater, but that’s where the communications media come into play: magazines, billboards, etc. There has to be something that conveys that status to the masses.”

For his part, Riedel remains steadfast. “There’s no chance that the theater will reclaim its lost glory,” he says. “(After) the rise of the Lloyd Webber-Cameron Mackintosh shows, theater was not dependent on actors anymore. The shows were the stars. I think theater has forever given up its hold on the cultural imagination in this country, sadly. It’s movies and TV now, people like Seinfeld. Or maybe the Internet.”

Telsey looks to crossover artists, that is, performers who make their mark in different media. “Philip Seymour Hoffman might achieve icon status,” he says of the stage (“True West,” “Long Day’s Journey Into Night”) and screen (“Capote”) actor. “That’s a guy who within the next few decades will be an actor everybody talks about.”

Perhaps more surprisingly, he also suggests actress Allison Janney. “Once ‘The West Wing’ is done and she takes stage and screen work,” he says, “she’ll be a Rosalind Russell-type who we’ll talk about many moons from today.”

Evered casts his eye on super-diva Cecilia Bartoli, the Italian mezzo-soprano whose recitals are always events. “She’s reaping the benefits of working hard early in her career,” he says. “And that’s paying off now. Of course, it helps being talented. But there are lots of talented people out there. The public responds to outreach. And it helps if you have a real life, if you’re seen as a real person, as Bartoli is.”

For those who scoff at these or other predictions, Turan has cautionary words. “Current popularity doesn’t necessarily matter,” he says. “It’s about longevity. You can’t tell who is going to last.”

But just because you can’t predict the future doesn’t mean you can’t worry about the present. And the state of film acting — the source for many icons of our time — troubles some. “Movie actors today all look alike,” says Riedel. “They’re all thin, sensitive and stubbled, and some have that gelled hair that looks greasy to me. And the women are interchangeable blonde dolls, with no really outstanding personality. I can’t imagine Reese Witherspoon achieving the status of a Carole Lombard, though Julia Roberts might.”

Beyond quibbling about quality, there’s the issue of separating wheat from chaff.

That’s especially difficult when it comes to movies, notes Turan, citing the avalanche of homevideo options. “In the old days, the people who ran revival houses and college film societies did the pre-screening for you. Now people have to do it on their own. So I think it may be more difficult for people to break through.”

Telsey, though, sees technology’s upside. “If anything, the digital age is giving people an easier way to become an icon,” he says. “Now I can do an audition in Dublin and two hours later, Julie Taymor can watch it in New York. Because of technology, I’m able to get in touch with people I’d never have been able to. It gives people more of a chance. It gives them access.”

Evered, however, wonders if some of the Internet’s excesses do more harm than good. “Does blogging build an audience?” he asks. “I wonder. It seems to me that you’re just getting more information to the same people, rather than bringing in new people.”

In the end, the whole process is like predicting the next decade’s fashions. Sometimes, we’re in for something entirely different, and sometimes, what’s old is what’s new. “It’s impossible to say how we will decide on future icons,” concedes Evered. “I think part of it is creating an illusion, and that’s getting harder.”