The three women come from different times, different lands and different wardrobe departments. But since they are all denizens of that quaint provincial theme park called Broadway, the green-skinned witch (hometown: Oz), the pink-cheeked tomboy (hometown: 19th-century Concord, Mass.) and the ethnic rainbow of a waif (hometown: Paris, but now adrift in 21st-century Brooklyn) turn out to share the same voice.

Close your eyes and listen as their larynxes stretch and vibrate with the pain of being an underdog and the joy of being really loud. Bet you can't tell them apart. For that matter, bet you can't distinguish the heroines of the current Broadway musicals "Wicked," "Little Women" and "Brooklyn" from the average female finalist on "American Idol."

When it's time for a big ballad on Broadway these days, theatergoers can pretend they are still in their living rooms, basking in the synthetic adrenaline glow of their favorite TV show.

Give the people what they already have. This reigning philosophy of Broadway has been translated into a multitude of musicals inspired by popular movies and vintage pop songbooks. So why not reality television?

"American Idol" also-rans have been dropped into Broadway replacement casts, including Tamyra Gray ("Bombay Dreams") and Frenchie Davis ("Rent"). "Brooklyn," Mark Schoenfeld and Barri McPherson's gooey fairy tale of street people and pop stardom, actually features a climactic "American Idol"-style sing-off between a pair of crowd-courting divas.

But such examples are superficial, the equivalent of a matron who piles hip-hop accessories on top of her St. John's suit. The tentacles of the "American Idol" sensibility actually reach much deeper, into the very throat of the American musical, and may change forever the way Broadway sings. This is not a happy prognosis.

The style of vocalizing that is rewarded on "American Idol" - by its panel of on-air judges and by the television audience that votes on the winners - is both intensely emotional and oddly impersonal. The accent is on abstract feelings, usually embodied by people of stunning ordinariness, than on particular character. Quivering vibrato, curlicued melisma, notes held past the vanishing point: the favorite technical tricks of "Idol" contestants are often like screams divorced from the pain or ecstasy that inspired them.

The Broadway musical has always had its share of big-voiced belters, from Ethel Merman to Patti LuPone. But they have usually belonged to the tradition of Broadway as a temple to magnified idiosyncrasies, to performers for whom song is an extension of individuality. Which is why when Simon Cowell, the most notoriously harsh of "American Idol's" judges, describes a contestant as "too Broadway," it is meant as a withering dismissal. Carol Channing, Robert Preston, Jerry Orbach and Gwen Verdon wouldn't stand a chance in the court of Cowell. And if they were starting out today, they probably wouldn't stand a chance in Broadway musicals either.

Like the Olympics telecasts, "American Idol" celebrates stamina, will power and gymnastic agility. The most successful contestants take an athletic approach to a melody. They hoist, hold and balance notes like barbells in a weight-lifting exhibition. And the audience claps and hoots instinctively every time such muscle-flexing occurs.

That same Pavlovian reaction is now being elicited on Broadway as well. Eruptions of note-bending have joined the hallowed list of performance tricks guaranteed to inspire applause: precision tap dancing, Rockette-style line kicks, handsprings, successive pirouettes and indignant one-liners that are followed by the slamming of doors.

At the performance I attended of the new musical "Dirty Rotten Scoundrels," , the audience greeted each number with subdued warmth, though the show's stars, John Lithgow and Norbert Leo Butz, were working hard to put over the songs with style and character. Finally, in a self-addressed valentine that is the show's last number, Mr. Butz claimed his "American Idol" moment with one musically stretched-out phrase: "I think we still deserve a ha-a-a-a-nd ..." I suspect that the composer David Yazbek intended the moment to be comic. All the same, the audience roared with approval . It was what they had been waiting for.

That self-congratulatory element is also part of the "American Idol" package - the subtext that goes, "I deserve to be a star because it's my right as an American, and because I try so hard." It seems appropriate that musicals as seemingly different as "Wicked," a politically corrected back story of "The Wizard of Oz," and "Little Women," adapted from the Louisa May Alcott classic, both have first-act finales that are brassy (and virtually interchangeable) declarations of self-worth and self-determination.

In "Little Women," the tomboy heroine Jo (Sutton Foster) bursts out with a number about her will to succeed called "Astonishing." In "Wicked," the maverick witch Elphaba (a role created by Idina Menzel, now played by Shoshana Bean) proclaims her independence in the ear-blasting "Defying Gravity." (A parody in Gerard Alessandrini's priceless spoof "Forbidden Broadway" has Ms. Menzel "defying audio.")

When it opened, "Wicked" also starred Kristin Chenoweth, as Elphaba's opposite, the popular and pretty Glinda (now portrayed by Jennifer Laura Thompson). Ms. Chenoweth is a sunny, witty singer who suggests a cross between Mary Martin and Bernadette Peters. If Ms. Menzel tackled her numbers, Ms. Chenoweth teased and flirted with them. The face-off between the witches of "Wicked" became a nightly confrontation between Old and New Broadway. It was Ms. Mendel who won the Tony and, from what I gather from parents of school-age children, the hearts of the little girls in the audience.

You could argue that Elphaba is a Broadway archetype: the unprepossessing, unlikely creature transformed into a powerhouse whenever she sings. Certainly that was the charm of Ethel Merman, who became a Broadway star in 1930 in "Girl Crazy." A half-century later, Jennifer Holiday was bringing down the house in "Dreamgirls" by wrapping her voice like a boa constrictor around an angry ballad called "And I Am Telling You I'm Not Going."

But there was something so distinctive as to be almost freakish about Ms. Merman and Ms. Holiday, as there often is about great performances in musicals. It's the spirit of uniqueness celebrated by the aspiring stars of "A Chorus Line" in the number "One," as in "one singular sensation."

By the 1980's, however, a homogenizing force had begun to steal over the Broadway voice. It started with the invasion of the British poperettas by Andrew Lloyd Webber ("Cats," "Phantom of the Opera") and the team of Alain Boublil and Claude-Michel Schönberg ("Les Misérables," "Miss Saigon"). Their swoony, ever crescendoing music required voices that were pretty and strong, but not much else. It seems appropriate that the ultimate Lloyd Webber star was Sarah Brightman, who possessed a register-testing but anonymous soprano.

Lord Lloyd Webber's spiritual heir in the United States, Frank Wildhorn, came up with cruder versions of the poperetta formula. "Jekyll and Hyde," "The Civil War" and most recently "Dracula" were costume musicals drenched in ersatz blood and ersatz passion. Though his characters were intense, as mad scientists and vampires tend to be, when it came to selling a song they all sounded pretty much the same, especially with their voices synthetically processed and amplified by the aural equivalent of Sensurround.

These folks at least had vitality, especially compared to the cipherlike sounds of the jukebox musicals that came to the fore in the 90's. Whether the source was rock opera ("The Who's Tommy"), feel-good rock 'n' roll (the songs of Lieber and Stoller, for "Smokey Joe's Cafe") or the sublime standards of Duke Elllington ("Play On"), the performers largely registered as cute, eager and personality-free, like peppy summer interns in a Disney World pavilion. Even singing gritty ballads like "On Broadway" or rock anthems like "Pinball Wizard," their voices came across as shiny, smooth and antiseptic, like those of grown-up Mouseketeers.

The upside for the producers of such shows is that their cast members are eminently replaceable. Sui generis stars are not necessarily advantages for investors hoping for long, sold-out runs. (And a full-scale Broadway musical needs to run and run and run just to break even.)

So it would seem to make good commercial sense to create musicals that put the emphasis less on individual performance than on overall concept, shows like the Abba musical "Mamma Mia!" or the Disney singing cartoons like "Beauty and the Beast."

Then there is that greatest of all obstacles to intimacy between audience and performers: the microphone, which "American Idol" contestants use as if it were a body part. Though miking has been ubiquitous for at least four decades, it still feels oddly primitive at most shows. It's often hard to tell where on the stage a voice is coming from. And while uncertain voices can sometimes be smoothed and bolstered by mechanical amplification, good voices are often roughened or neutered by the same process.

It's not that the American musical is an ossified form that can accommodate new musical styles only through forced grafting and transplant. The real problem with the blandness of Broadway singing lies less in the material than in the execution. The rock musical "Rent" is filled with sugary pop effervescence. But most of its original cast brought quirky and specific interpretive intelligence to their roles.

In "Dirty Rotten Scoundrels," Mr. Butz delivers a hip-hop love song to material luxury that happily trades on the exuberance of the very style it satirizes. And in the title role of the Disney "Aida," Heather Headley found expressive emotional magic in Elton John-Tim Rice songs that seemed natural candidates for the "American Idol" approach of feelings-by-the-numbers.

Bernadette Peters, Audra MacDonald, Betty Buckley, Mandy Patinkin, Tonya Pinkins, Michael Cerveris, André De Shields, Mr. Butz and Ms. Chenoweth, among others, have all demonstrated that it is possible to go pop on Broadway without sacrificing individual flair. (And to be fair, "American Idol" has produced at least one star - Fantasia, last year's winner - with a voice and approach of her own.)

We must cherish such performers. Good, well-trained voices that can carry a tune and turn up the volume come cheap. What does not is the voice that identifies a character as specifically and individually as handwriting.

It's what you hear every time Barbara Cook, the 50's Broadway ingénue and enduring concert artist, sings a number by Stephen Sondheim or Harold Arlen. Ms. Cook has a ravishing soprano. But a great Broadway voice doesn't have to be pretty. Floating on a stream of exquisite sound is easy. Finding in that sound all the kinks and bumps and curls that make a person fascinating, exasperating and unique is what transforms a Broadway musical from a cookie-cutter diversion into ecstatic art.