British "American Idol" judge Simon Cowell smiles during the Concert for Diana at Wembley Stadium in London, in this July 1, 2007 file photo.[Photo/Agencies]

"American Idol" made Simon Cowell a household name in the United States, but the prickly British music Svengali is hitting some flat notes as he tries to launch his own TV singing competition.

Cowell, 51, has been working on a U.S. version of his hit UK talent show "The X Factor" for more than 18 months. But as the clock winds down to its much-hyped debut in the fall, he is facing some last-minute challenges.

His personal pick for the judging panel -- British singer Cheryl Cole -- was reportedly dumped from the lineup, possibly because of her thick accent. She was also dropped this week from the panel of the UK version of "The X Factor".

Perhaps more ominously yet another singing show, "The Voice," has become a surprise hit by borrowing some key "X Factor" components.

TV pundits also wonder whether viewers have the appetite for another months-long singing competition. "X Factor" will join a list that includes "The Sing-Off," "Platinum Hit," "The Glee Project", "American Idol", and Cowell's own "America's Got Talent."

Last month, Fox television touted Cowell and "The X Factor" as the highlight of its new fall schedule. Fox Networks Group chairman Peter Rice described Cowell as "the absolute star of the genre at the pinnacle of his game."

Two weeks later, something had clearly gone wrong after two rounds of auditions before Cowell, Cole and fellow judges Paula Abdul, record producer Antonio "L.A." Reid.

Cole was seen as an odd choice: A style icon and a household name at home but unknown in the United States.

Depending on whom you believe, Cole was apparently dropped because of concerns that her Northern English accent might prove tough for U.S. viewers, or because she lacked chemistry with "Idol" alumna Abdul, or because she was uncharacteristically nervous when "X Factor" shooting started.

"To get so far and discover it is not working -- that is a little bit of a shock," said Michael Slezak, senior editor with TVLine.com.

"But expectations are so high that if some key element isn't working, it doesn't shock me that they are not worried about personal feelings and are making whatever changes they feel necessary," Slezak said.

TOO MANY TV TALENT SHOWS?

Fox and Cowell's Syco production company have declined to confirm reports that ex-Pussycat Dolls singer Nicole Scherzinger -- initially hired as "X Factor" co-host -- will take over from Cole.

They also declined to comment on whether any re-shoots will be necessary, or how production has been affected.

"It could be a very big setback because the Fox marketing machine been pushing 'X Factor' since January," said Craig Tomashoff, a TV writer for Xfinity and TV Guide. "Cole was Simon's pet project and now she has gone. I am certain that's not how everyone at Fox envisioned it would work."

But Tomashoff said the bigger issue might be a surfeit of talent shows, "and in the fall there are also a lot of other new TV shows that people are beginning to check out."

While Cowell was working on "X Factor," rival network NBC jumped in with "The Voice." Making its debut in April, it boasts a stellar coach/mentor lineup of Christina Aguilera, country singer Blake Shelton, R&B star Cee Lo Green and Maroon 5 front man Adam Levine -- who also perform together on the show.

The audience for "The Voice" has grown, reaching a high of 14 million viewers on Tuesday. Perhaps more significantly, it adopts two of "X Factor"s distinguishing features -- celebrity coaches compete against each other to mentor contestants, and auditions are held in front of a live audience.

"The success of that show has got to make Fox and Simon a little bit nervous. You don't want someone getting into the market before you," said Slezak.

But he noted that the Cheryl Cole debacle has kept the show in the headlines. "How many shows premiering in the fall would kill to have people and the media talking about them every single day?", he said.

Indeed don't count out Cowell just yet, Tomashoff warned. "I don't think he takes losing very well. If anything, this will fire him up even more,"

Fox is a unit of News Corp; NBC is controlled by Comcast Corp; the UK version of "X Factor" is broadcast on ITV