LOS ANGELES (Reuters) - Grammy-winning pop star Mariah Carey will join Fox television's "American Idol" singing contest as a judge next season as the highly rated show fights to regain its slumping audiences.

Kevin Reilly, president of entertainment for Fox Broadcasting, told television critics on Monday in Los Angeles that popular singer Carey will be one of the replacements for departing judges Steven Tyler and Jennifer Lopez.

Tyler, the front man for rock band Aerosmith, announced his exit earlier this month to focus on his revived music career. Lopez, too, has hinted at her departure in recent weeks and, on Monday, Reilly confirmed she will not return for the upcoming season.

"I can say it is 100 percent that Jennifer won't be back to the show," Reilly said.

Reilly said the deal with Carey was finalized early on Monday and, in a dramatic move for TV critics at the conference, he called the singer on his cell phone to announce the deal.

"Hi Mariah. How are you? I have just uttered your name for the first time. We do have a deal, don't we?" Reilly said.

Carey, answering on speakerphone, said: "I am so excited to be joining 'Idol'... I wish I could have been there myself to tell you, but this all kind of just happened. I can't wait to get started."

Reilly declined to comment on the status of Randy Jackson - the only original member of the show's judging panel - but said he expected to announce a second new judge within the next two weeks, adding that some of "the biggest names in the business are interested in doing the job."

One-time "American Idol" runner-up Adam Lambert has been mentioned in the entertainment media as a possible contender for one of the new jobs.

Carey, 42, known for soaring ballads like "Hero" and "We Belong Together," had been named in reports as a frontrunner and she is expected to bring attention and viewers to the 11-year-old singing contest, which lost some 20 percent of its audience this past season.

CAREY ALREADY A MUSIC IDOL

The singer has won five Grammys, the music industry's top honors, and she sold more than 200 million records worldwide. She is currently working on a new album and plans to release a lead single - "Triumphant" - next month.

"American Idol" creator Simon Fuller said Carey "defines the word 'Idol' and will inspire every singer that has the honor of performing in front of her."

Reilly did not discuss the financial details of the agreement, but Carey previously has been reported to be in negotiations for a payday of around $15 million a year.

Carey, who was courted last year by Simon Cowell for the U.S. version of his "X Factor" singing show, joins a roster of superstar celebrity judges on reality TV. Britney Spears was signed earlier this year for Fox's upcoming second season of "The X Factor" and "shock-jock" Howard Stern joined NBC's summer series "America's Got Talent."

"American Idol" has been a ratings and advertising juggernaut since it debuted in 2002 and has been the most-watched entertainment program on U.S. television for nine consecutive years. But its audiences are now only about half the more than 30 million who watched regularly in the show's 2005 and 2006 heyday.

The most recent season finale in May was the least-watched in "America Idol's" history, attracting just 21.5 million viewers.

Executive producer Nigel Lythgoe told journalists earlier on Monday that he thought "Idol" should swap judges every season, partly to accommodate the careers of top artists.

Reilly declined to speculate about that possibility, but he told journalists that "Idol" is "12 years old now. We need to keep it fresh."

The show returns with Carey and at least one other new judge for a 12th season in January 2013.