Broadway fortunes get a boost when ‘American Idol’ exes join casts.

SHE was already a big star, adored by millions. But when it was announced that she would make her Broadway debut this spring, the anticipatory buzz went through the roof.

Ads with her name splashed in large, bold type popped up all over New York City. A mad scramble for tickets erupted. Fans squealed the moment she stepped on stage. Crowds mobbed her at the stage door, clamoring for autographs and pictures. And producers of the show rejoiced in their financial good fortune.

But all this fuss isn’t over movie star Julia Roberts and her theatrical debut in “Three Days of Rain.” One of the hottest marquee draws on Broadway this year is Diana DeGarmo, who is appearing in a supporting role in the musical “Hairspray.”

Diana who?

If you have to ask, you’re probably not one of the 31 million viewers who tune in to or TiVo “American Idol” every Tuesday and Wednesday, making the singing contest not only television’s top-rated show but also a cultural phenomenon.

“Idol” has spawned numerous imitators. Its far-reaching influence has drawn in seasoned entertainers, such as Rod Stewart and Barry Manilow, seeking to reinvigorate their careers -- as well as boost their own record sales. Then there’s the record deals -- not only for the winners but also for the losers; “Idol” concert tours; movie roles; trivia games; perfume; shower radios; and Pez dispensers.

And now class is trying to cash in on flash.

“Theater of the 21st century needs to appeal to a younger generation,” says “Hairspray” producer Margo Lion. “ ‘American Idol’ has certainly brought in audiences -- people are dying to see these performers. It brings in a hip factor, just like Disney brought in family audiences.”

Of course, success isn’t always guaranteed. Last week, 2003 finalist Josh Strickland made his Broadway bow in the title role of Disney’s “Tarzan,” which opened to very mixed reviews. Strickland’s debut on the Great White Way followed triumphs by earlier “Idol” castoffs DeGarmo, Frenchie Davis and Tamyra Gray. Davis, who was bounced from the series in 2003 following revelations that she had once worked for an adult website, landed a role in “Rent,” with a featured solo in the musical’s anthem “Seasons of Love.” First season also-ran Gray appeared in the musical “Bombay Dreams” in 2004.

“ ‘American Idol’ has absolutely become a big deal here in terms of finding new talent,” says New York casting director Bernard Telsey, who placed DeGarmo, Strickland and Davis in Broadway shows. “Watching this show has become another way to locate incredibly talented people -- it’s like a televised open call. I watch it, and certain people on our staff have to watch it. Our inside joke is we root for our favorites to lose so that they can become available to us.”

No longer can acerbic judge Simon Cowell’s criticism of being “too Broadway” be considered a slap in the face. MTV’s “Total Request Live” may have closed its doors to these “Idol” wannabes, but the Great White Way is laying out the welcome mat -- and with good reason.

After losing a singing showdown to Fantasia Barrino last year, DeGarmo, who had performed in theater in Georgia (“but nothing really huge,” she says), appeared in “West Side Story” in San Jose. Last February, the 19-year-old DeGarmo joined the cast of the 2003 Tony Award-winning “Hairspray,” playing not the leading role in the ‘60s-era musical based on the 1988 John Waters film, but the smaller part of Penny Pingleton, a perky and slightly clueless teen. Just before DeGarmo signed on, “Hairspray’s” net receipts were about $465,000, reported Variety. Her first week in the show, box-office figures jumped to $530,000, then $673,000, topping $855,000 for the second week in April.

When Davis first joined “Rent” in the spring of 2003, there was a noticeable boost in the box office, according to producer Jeffrey Seller.

“I really didn’t know who she was, but my staff said we needed to get her,” he recalls. “I didn’t think an ‘Idol’ contestant would sell tickets. But lo and behold, for her first four months, we saw a rise in sales of about 20%. Frenchie had an immediate impact. People wanted to see her sing ‘Seasons of Love.’ ”

But the theatrical tentacles of “American Idol” stretch far beyond New York’s Times Square.

Amy Adams, a finalist from the 2004 season, is making her theatrical debut in a touring production of “Joseph and the Amazing Technicolor Dreamcoat,” which opens July 11 at the Orange County Performing Arts Center. Jennifer Hudson, an “Idol” finalist last year, is in the upcoming film of the Broadway hit “Dreamgirls.” “Rent” continues to audition “Idol” contestants. A production of “Ain’t Misbehavin’ ” with former “Idols” is in the works. And producers of “The Color Purple” have also shown interest in contestants.

“The show is a very legitimate venue for talent,” Seller says. “The whole thing may be totally insipid, but in a culture where it seems that football and basketball are our most important competitions, it’s very heartening when the highest-rated show in America is a competition of singers. It’s a good thing for the culture, and I can’t help but think it’s a great thing for those of us who work in the world of live performance.”

The road to Broadway has become so lucrative that key “American Idol” honchos are advising contestants to explore a range of opportunities. “Many of these kids come in with tunnel vision, saying they want a hit record, and I’m telling them now there are more ways to have a wonderful career,” says Debra Byrd, “Idol’s” vocal coach and vocal arranger, who has guided each of the show’s contestants since the series started in 2001.

Byrd says she’s already positioning one of this season’s three remaining finalists, Katharine McPhee, as a Broadway prospect. “She’s got real potential,” says Byrd, adding that after first hearing McPhee sing, she told the contestant that she sounded “like a gifted theater singer.”

DeGarmo admits that her “Idol” past can provoke tension at times: “A lot of people in the industry don’t think you can back it up. I’ve really enjoyed the challenge of having to prove myself. There comes a point where you have to stand on your own two feet rather than use that show as a crutch. I’m glad I didn’t win ‘American Idol.’ It wasn’t meant for me to win. And I think I’ve paid my dues. If anyone wants to challenge me on that, tell them to bring it on.”

Despite her theatrical success, she isn’t abandoning her pop star dreams: “My next thing is winning a Grammy.”

DeGarmo ended her run in “Hairspray” this week to embark on a national tour of “Brooklyn: The Musical,” in which she’ll play the title role. On Sept. 8, she’ll return to “Hairspray.”

For Davis, being on Broadway “was always the ultimate goal. I was a theater major in college. My goal was not to be a pop star. I went on every audition I could, and I just saw ‘American Idol’ as just another audition.”

Making her debut in “Rent,” she says, was “an amazing experience. There are no words to describe how amazing it is to be part of this show. I’ve enjoyed my life and being on Broadway.”

But don’t ask her too much about “American Idol.” She doesn’t watch it -- and she really doesn’t like to look back.

“It comes up a lot. That may be how people define me, so I don’t talk about it. I want them to see there’s so much more to me,” she says. “I’ve moved on.”