HOLLYWOOD – Tom DeLay might be a wild thing on the dance floor, but when it comes to ratings, he seems to have two left feet.

The former Republican congressman was supposed to spice up this season of “Dancing With the Stars,” but it hasn’t worked out that way. In fact, the dance-competition show, a bulwark of ABC’s schedule, is shambling through its worst season since it premiered in summer 2005.

DeLay – who created a mild sensation when he and partner Cheryl Burke did the cha-cha to “Wild Thing” – dropped out last week because of injuries, joining Debi Mazar, who was voted off. That will leave this season’s fate in the hands of remaining luminaries including Donny Osmond, Kelly Osbourne and Melissa Joan Hart.

The ratings pose a worry for ABC, which has been helped through some difficult times by “Dancing.” Last year, when executives brought back several second-season scripted series that tanked, the ballroom dance-off helped keep ABC competitive overall – in fact, the network was ranked No. 1 among young adults at this point in the season. Now, ABC is locked in a three-way tie for first with CBS and Fox.

“Dancing” still pulls enviable numbers, with an average of 17 million viewers, according to the Nielsen Co. But that’s a dip of 13 percent compared with the same period last year. Among adults ages 18 to 49, the viewers advertisers court most, the show has slipped 19 percent.

During fall 2007 – crowned with highlights that included Marie Osmond passing out as the judges critiqued her samba – “Dancing” leaped to its most-watched season, averaging 21.7 million viewers.

So what happened? ABC officials concede that, the competition, particularly from Fox’s medical drama “House,” is stronger this year.

But many analysts and fans believe the cast – which hews to “Dancing’s” time-tested formula of faded stars, pro jocks and bizarre wild cards – simply hasn’t gelled this year. The inclusion of DeLay, a fiercely partisan former House majority leader who left Congress after indictment on campaign-finance charges in 2005, touched off a flurry of amused interest.

Many ordinary viewers, however, probably had no idea who he was.

Other cast members, including Osmond and Hart, likewise owe whatever renown they possess to achievements years since passed. Hart’s “Sabrina the Teenage Witch” ended its ABC run a decade ago.

“This cast probably is not as interesting as the casts they’ve had in the past,” said Scott Sternberg, a reality producer and “Dancing” fan. “You have to connect with one of the players and root for them.”

It also hasn’t helped that the cast has been reasonably well-behaved, not what viewers usually look for on an unscripted competition show. During Season 7, Cloris Leachman, then 82, endeared herself to viewers with scandalous antics, including grabbing the crotch of partner Corky Ballas during the mambo.

“This is the worst season ever,” a comment on a Los Angeles Times’ message board said last week. “Now I can go to bed early on Monday and Tuesday nights. Thanks for the extra beauty sleep.”

But Andy Donchin, an executive vice president at New York ad company Carat USA, warned that it’s too early to write off “Dancing.”

“It’s still an extremely attractive show,” he said. “Most shows show a little bit of a decline in the ratings after awhile.”

Sternberg said that “Dancing,” like “American Idol,” might need some rejiggering. He suggested more taped pieces showing the dancers rehearsing and giving cohosts Tom Bergeron and Samantha Harris more to do.

“You need to mix up that formula a little bit, freshen things up,” he said.