Will Britney Spears rescue Cowell's 'X Factor'?

Britney Spears makes her debut this week as the biggest celebrity judge on US television in a revamped version of "The X Factor" that is looking for its own special something in a stepped-up ratings battle with "The Voice."

In what TV pundits expect to be a tough contest for the most viewers, "The X Factor" returns to Fox television for a second season on Wednesday, after "The Voice" moves to the fall slot on NBC for a three-night season opener, starting on Monday.

Spears, 30, was tempted to join "The X Factor" by a reported $15 million salary after a 14-year singing career that made her the world's biggest pop phenomenon of the 2000s.

"X Factor" creator Simon Cowell is banking on her huge fan base and a strong curiosity factor to give his show a second chance with audiences after a disappointing first season in 2011 that attracted about 12.5 million viewers, and ended with the firing of two judges and the host.

"The Voice," which was watched by an average 15.6 million Americans last season, gets off to a rocking start on Monday with judges Christina Aguilera, Cee Lo Green, Adam Levine and Blake Shelton performing a cover of Rolling Stones hit "Start Me Up."

On Wednesday, the rival shows will compete head-to-head in a late programming move by NBC that Cowell condemned last week as a mean-spirited spoiling tactic.

"I think it's going to be a really tight race. At most, a big name gives a little pop in the ratings at the beginning," said James Hibberd, senior entertainment writer with Entertainment Weekly.

"But the celebrity judges are there to perform every bit as much as the people on stage, and their charisma and their wit need to be compelling to the audience," Hibberd said.