LOS ANGELES » It’s one of the few shows on television that tells viewers exactly what they are going to get: "Dancing With the Stars."

But just who are the stars?

These days it’s not so easy to tell. When ABC started broadcasting this sequin-encrusted competition in 2005, the celebrities were clearly defined. They were the spray-tanned actresses (Kelly Monaco of "General Hospital"), fluid athletes (Apolo Anton Ohno, Emmitt Smith) and boy-band members (Lance Bass) who risked humiliation each season as they took dancing lessons from an unknown cadre of ballroom professionals.

Six years later the construct of "Dancing With the Stars" is being turned on its head. In some ways those pros — "Cheryl! Maks! Derek!" — have now become the headliners. The increasingly C-list celebrities lined up to participate have found they are no longer alone in the spotlight.

"There is this weird inversion of what the show was meant to be," said Conrad Green, an executive producer of the show. "Now when our celebrity competitors meet their dance partners, it’s the celebrity who is star-struck."

That’s exactly what happened when the former talk-show host Ricki Lake, a competitor on the current season of the show, met her professional partner, Derek Hough. "When I walked in and saw Derek, I melted a little bit," she told the audience.

Some of the show’s professional dancers now have such big fan followings that "to some degree they are responsible for keeping their celebrities on the air," said Tom Bergeron, the show’s co-host. "People at home sometimes vote more for the dancer than the star."

"Dancing With the Stars" returned last Monday for its 13th installment (two a year are produced) and attracted an estimated 19 million viewers, an 11 percent decline from last fall’s premiere, according to Nielsen. The pressure is on the aging series to compete with new Monday-night competition from a rejuvenated "Two and a Half Men" on CBS and "Terra Nova," an expensive science-fiction series on Fox.

"Dancing" is counting on interest generated by competitors like David Arquette, Nancy Grace, Lake, Elisabetta Canalis (a model and actress best known for dating George Clooney) and Rob Kardashian, one of the lesser-known members of that reality-television clan. The casting of Chaz Bono, the transgendered son of Cher and Sonny Bono, has already resulted in a cascade of media attention.

But the star power this season is less than in previous ones, when guests like Kirstie Alley, Jennifer Grey and Donny Osmond competed. The lack of marquee names reflects the difficulty producers are having in landing high-wattage celebrities willing to endure the rigors of the series. Bill Clinton on Tuesday revealed during a talk-show interview that he had considered competing but "didn’t have the time to train."

To some degree Green and ABC are counting on the show’s better-known professionals to pick up the slack. Hough (pronounced huff), a blond heartthrob who is a three-time winner of the series, returned to "Dancing" last Monday after taking a season off to work on a movie. ("It’s the return of the Hough!" an announcer shouted during the telecast.)

"It’s just like with a hit sitcom or drama, I guess," Hough said in a telephone interview. "Viewers really get to know and love the regulars, and guest stars come and go."

In recent seasons producers have increased efforts to position the professional dancers as archetypes who will pop with the audience. Maksim Chmerkovskiy, known to "Dancing" viewers for his no-nonsense teaching style and waxed chest (perhaps not in that order), is "the bad boy of the ballroom," according to Bergeron. Cheryl Burke, a two-time winner of the series, is a live wire — all curves and flying hair and attitude.

Kym Johnson, a long-legged Australian and two-time winner of the competition, is the girl next door. "We put a lot of pressure on ourselves — I literally ended up nearly breaking my neck last year — and I think the audience has come to recognize that," Johnson said. Her neck injury was one of the shows biggest story lines last season, played up by producers in flashback montages and testimonial videos.

As part of establishing regulars like Burke and Chmerkovskiy as characters, producers have given them more screen time. The show takes cues about whose popularity is soaring from things like coverage of them in traditional and tabloid media outlets, audience response and their growing Facebook and Twitter followings.

ABC wants to use its well-known pros — a group that also includes Tony Dovolani, Mark Ballas, Anna Trebunskaya and Lacey Schwimmer — to keep loyal viewers coming back, but it doesn’t want to build them up so much that they can hold the show hostage for bigger salaries. ABC declined to comment on compensation, but agents say the veteran dancers earn an estimated $10,000 to $12,000 a week.

The network has various levers to keep the dancer in line. Producers cycle in new professionals (a reminder that there is a ready and available pool of replacements) and give the pros no say in their pairings. Getting a little full of yourself, Cheryl? Perhaps you’ll be dancing with Tom DeLay.

Still, there is no doubt the pros have come a long way since the show’s early days, when they were seen more than heard. Green said the pros were initially viewed more as "horses for courses," dancers who fit the needs of the celebrity partner.

"In the beginning it was only about the celebs, and we would be in their shadow," Burke said. "They are following in our footsteps now. I’m assuming that a lot of them come in with casting requests: ‘I will participate, but I have to have this pro as a partner."’