LOS ANGELES (Reuters Life!) – CBS has claimed an early victory as the most-watched US television network for the 7th time in eight years in the 2009-10 prime-time season, which ends this week.

But Fox's "American Idol" will wind up the No. 1 program for the 7th year in a row, and it has drawn the most viewers in the 18 to 49-year-old demographic group most coveted by advertisers, according to data from TV tracker Nielsen.

With three days to go before the official end of the 2009-10 season, ABC and NBC are battling it out for third place for overall viewers. But ABC is on track to finish second to Fox among adults 18 to 49.

Audience figures for the week ending May 23 show CBS with an average nightly audience of 11.7 million in prime-time, followed by Fox (9.9 million), ABC (8.6 million) and NBC (8.2 million).

CBS, a unit if CBS Corp, notched the top two comedy series with "Two and a Half Men" starring Charlie Sheen, and "The Big Bang Theory."

It also dominated the drama category, with "NCIS" ranking as the No. 1 scripted program, and it scored the top three new shows of the season with reality program "Undercover Boss", crime series spinoff "NCIS: Los Angeles" and legal drama "The Good Wife" starring Julianna Margulies.

Despite about a nine percent drop in average audiences this year for "American Idol" on News Corp's Fox, the singing contest remained the most-watched show with 23.9 million viewers. The network's new musical comedy "Glee" was the highest-rated, new scripted series among 18 to 49-year-olds and 18 to 34-year-olds. It has shown a 68 percent increase in total audience to an average 12.3 million viewers this spring, compared to its debut in the fall of 2009, Fox said.

Fox has ordered a third season of "Glee" for 2011-12.

Despite bumper Winter Olympics ratings for NBC earlier this year, the network is struggling to avoid finishing at the bottom of the four major networks once again as it revamps its depleted slate of scripted shows. NBC is part of the media division of General Electric Co.