* Fox down 20 percent in 18-49 demographic
* Network bottom of big four U.S. networks in total viewers
* No news on Britney Spears future with "X Factor"
By Jill Serjeant
LOS ANGELES, Jan 8 (Reuters) - Fox entertainment chairman Kevin Reilly on Tuesday acknowledged that his TV network had struggled to find an audience last season but said he hoped for a better performance going forward.
"We limped our way in after 2011. Nobody is happier than us to get into a new year where hopefully there are better things to come," Reilly told television reporters.
Fox television, a unit of News Corp, has slumped from long-running king in the 18-49 demographic prized by TV advertisers to current third place.
In the season so far, Fox has lost some 20 percent of its 18-49 audience compared to the same point last year, while rival NBC has pulled out of a nine-year slump and is in first place.
Fox is also currently at the bottom of the big four U.S. broadcasters in terms of total numbers of viewers.
"We are struggling right now because we didn't put on a big hit (in the 2012 fall season)," Reilly said.
Reilly said the TV industry was healthy, despite most networks losing audiences who tune in regularly to TV shows.
But he bemoaned the current system that still largely measures audiences watching TV on a nightly basis and fails to take in those watching on streaming websites, DVRS, the Internet and outside regular prime-time hours.
"The ecosystem of TV is as vibrant, if not more so, than ever before. There is more choice, more quality and breadth of quality on TV," he said.
"Our ability to market and measure those audiences has changed drastically," he said. "Hopefully, soon we can roll up all the ways people watch and says 'there's our audience'."
Fox has high hopes for new serial killer drama "The Following" starring Kevin Bacon later in January, and for the return on Jan. 16 of "American Idol" with new judges Mariah Carey, Nicki Minaj and Keith Urban.
New Fox comedies "The Mindy Project" and "Ben and Kate" failed to gain traction with viewers last fall, while talent show "The X Factor" lost some three million viewers compared to its 2011 debut, despite the addition of pop star Britney Spears to the celebrity judging panel.
Several TV critics found Spears bland and boring on the show, and rumors have already begun to swirl about her being replaced before "X Factor" returns for a third season in September 2013.
Reilly said he was unaware of any decisions by the show's creator, Simon Cowell, about the panel, but said the network would be happy to have Spears back.
"Next year, I don't know. Simon has been on vacation, he was exhausted. He hasn't even talked about it," Reilly said of the "X Factor" panel.
In the 2012-13 TV season to date, NBC, a unit of Comcast Corp, is the most-watched network among 18-49 year olds, followed by CBS, Fox and ABC.
CBS, a unit of CBS Corp, is top in total viewers, followed by NBC, ABC and Fox, according to ratings data.