UPDATE 1-Lambert, Allen duel for 'American Idol' crown

* Adam Lambert, Kris Allen sing in final performance show

* Contestants sing three songs each in live telecast

* Winner to be announced Wednesday in finale

(Recasts after final performances)

By Nichola Groom and Alex Dobuzinskis

LOS ANGELES, May 19 (Reuters) - "American Idol" finalists Kris Allen and Adam Lambert strutted their stuff in search of votes for the last time on Tuesday in a TV show singing contest host Ryan Seacrest dubbed "the guy next door versus the 'guyliner.'"

Lambert, a flamboyant musical theater performer with a fondness for wearing eyeliner, and Allen, a clean-cut acoustic guitar player, each sang three songs in their final bid to take the 2009 "Idol" crown and win a recording contract.

After 100,000 people auditioned last summer and five months of broadcasts on the Fox network, the winner will be chosen by viewers' telephone votes and announced at the end of a finale on Wednesday night.

Lambert, 27, who was widely considered the front-runner heading into the finale, reprised one of his best-received performances of the season, singing "Mad World," while Allen, 23, sang "Ain't No Sunshine" by Bill Withers.

"Idol" judge Simon Cowell dubbed the first round a victory by Allen, admitting that he had doubted whether the 23-year-old belonged in the finale.

"When your name was announced last week I wasn't sure whether America had made the right choice," Cowell told Allen. "But I absolutely take all that back now."

For their second songs, the contestants performed selections chosen by "American Idol" creator Simon Fuller. Lambert sang "A Change is Gonna Come" by Sam Cooke, receiving universal praise from all four judges. Allen followed with Marvin Gaye's "What's Going On," for which he got mixed reviews.

"A million percent Adam," Cowell declared.

For their final songs, Lambert and Allen performed their own versions of an original song called "No Boundaries" that was co-written by judge Kara DioGuardi.

DioGuardi said she hoped Allen wouldn't be judged on that song, saying it was too high for his vocal range. For Lambert, it was more praise from the usually hard-to-please Cowell.

"The whole idea about doing a show like this is that you hope you can find a worldwide star -- I genuinely believe with all my heart that we have found that with you."

"American Idol" began as a cheesy summer talent show in 2002 but quickly morphed into a cultural phenomenon that attracts tens of millions of viewers a week to News Corp's (NWSA.O) Fox network.

It has generated a long list of stars from its winners and losers, including singers Kelly Clarkson, Carrie Underwood and Chris Daughtry and Oscar winner Jennifer Hudson.

Ratings have sagged 7 percent this season to about 26 million viewers an episode, but it remains the top-rated U.S. show.

(Editing by Eric Beech)