Fox takes so seriously the allegation that "American Idol" judge Paula Abdul had sex with one of the contestants during the competition that the network has gone and put her on yet another reality series.

On the other hand, the network has hired Acme Independent Counsel to conduct a thorough investigation as to whether Abdul coached second-edition finalist Corey Clark on his performances and seduced him, as Clark claims, when he's not busy being arrested for getting into food fight with his manager at a hotel, or promoting the release of his new song "Paulatics," about that alleged affair.

"The credibility of that competition is extraordinarily important to us," Fox Entertainment President Peter Liguori said Thursday at Summer TV Press Tour 2005. "We want to make sure there is a thorough investigation into what we've seen on ABC," he said, referring to the May "Primetime Live" report "Fallen Idol."

This independent counsel -- Liguori declined to name the person or firm -- was hired last month by the network and "Idol" producers to look into charges Clark made in an interview on the ABC newsmag about his relationship with Abdul.

The reality series, which will begin its fifth edition in January, is Fox's most important franchise. Airing two nights a week, it has transformed Fox into the most watched network among the young viewers whom advertisers pay the most to reach.

The investigation is "winding down," Liguori told critics, but it would not be rushed to be finished before tryouts for the next edition begin on Aug. 18.

Asked why it's taking so long, Liguori said the investigators were interviewing "corroborating witnesses."

"We want to make sure we're being thorough," he said, adding, "The credibility of this competition to us can never be underestimated."

"Are you saying that, given the importance of the credibility of 'American Idol,' Paula will be a judge on the show . . . if this investigation is not wrapped up by August?" asked one dumbfounded critic.

"We're in the television business," Liguori said, stating the obvious. "I don't think anyone should be held to a standard higher than the judicial system. At this point we have nothing that specifically says that she shouldn't be showing up for work."

That's also his thinking behind adding Abdul, who got her start as a choreographer, to Fox's dance competition series "So You Think You Can Dance," which debuted last week.

"Given the fact that we were in the throes of the inquiry, Paula was just a natural for the show," Liguori said. In announcing the addition of Abdul, the network said she would "use her unique skills of dance and motivation to teach real people how to find their groove thing and really shake it."

The results of the investigation will be made public, Liguori said. But he declined to say whether Abdul would be sacked if she was found to have coached Clark and had sex with him while he was in the competition. He said he did not want to speculate and added, "The credibility of that competition is incredibly important to us."

Fox has rules about producers or judges fraternizing with contestants on reality series, Liguori assured critics. But they are "all geared toward: Is, in fact, a judge or any of the producers affecting the outcome of the show?' " And on "Idol," he noted, "ultimately it's America that decides on who moves forward."

"That said," he added, "the credibility of the competition is Job One for us."

One critic noted that when CBS News investigated itself, it named those doing the investigation, while Liguori was keeping the identity of his "independent counsel" under wraps.

"What exactly in your mind is the difference between a news report and a television show that people want to feel is credible?" asked one critic.

"News talks about true life-and-death situations and we're talking about a piece of entertainment here," Liguori responded.

Then he quickly added: "With all that being said, we're clearly not making light of the allegations.

"We're taking the credibility of the show as being paramount to us."

British producer James Goldston, whose documentary "Living With Michael Jackson" delivered boffo ratings for ABC two years ago, has been named executive producer of ABC's struggling "Nightline."

Goldston, who joined ABC News last year as a senior producer of prime-time specials and investigative reports, replaces Tom Bettag.

Bettag announced earlier this year that he would step down, along with host Ted Koppel, in December. The duo decided to leave together after Koppel and ABC executives disagreed over the future shape of "Nightline," which may turn into a live, one-hour program covering a number of topics each night. Currently, Koppel hosts three nights a week and the show usually is taped.

The late-night program has been experimenting with different formats and hosts as it tries to reverse its downward ratings trend. On the nights when Koppel is not anchoring, the show has gone with a multi-topic format.

This year, "Nightline" is averaging 3.4 million viewers, down more than 1 million from four years ago. In 2002, ABC executives made a clumsy, and ultimately unsuccessful, attempt to replace it with a late night comedy show hosted by David Letterman.

"Nightline" evolved out of the Iranian hostage crisis in 1979, when Koppel anchored a nightly show called "America Held Hostage." The show started in earnest as "Nightline" on March 24, 1980, with Koppel hosting live.

Goldston will continue to live in New York, but ABC spokeswoman Emily Lenzner said there are no plans to move the Washington-based show. "He's going to be flying back and forth a lot on the shuttle," she told The Post's John Maynard.

Before joining ABC in 2004, Goldston was executive producer of the British public affairs show "Tonight With Trevor McDonald," where he produced a number of documentaries including "Living With Michael Jackson."

ABC News paid about $5 million for first U.S. broadcast rights to the documentary by British journalist Martin Bashir, and aired it on the newsmagazine "20/20" in February 2003. It drew more than 27 million viewers, making it the most-watched newsmagazine since Barbara Walters's interview with Monica Lewinsky in March 1999.

It's full speed ahead for judge Paula Abdul of "American Idol," despite Corey Clark's tale of an affair with her.