LOS ANGELES (Reuters) - CBS on Tuesday declared victory in the 2011-12 television season, saying it was the most-watched U.S. network for the 9th year thanks to hits like crime drama "NCIS" and the nation's top comedy "The Big Bang Theory".

Although three nights remain of the current TV season, CBS said it would win first place in total viewers by the largest margin by any network in 23 years.

According to the most current Nielsen ratings data, Fox will win the season in the 18-49 age group coveted by advertisers, although it has seen a nine percent drop in those viewers in the past year.

While CBS dominated scripted drama and comedy, Fox said it still has the nation's most-watched show with "American Idol," despite the singing contest losing around 23 percent of its total audience this year.

CBS is projected to end the season with an average 11.74 million total viewers, on average, per night, followed by Fox (8.87), ABC (8.36) and NBC still in 4th place at 7.38 million.

Fox is first in the 18-49 demographic, despite losing 9 percent of those viewers compared to last season. CBS was second, NBC grew 9 percent to come in third and ABC was fourth.

CBS owed its victory to having nine of the 10 most-watched dramas on television, led by "NCIS", "NCIS: Los Angeles", and "The Mentalist". The network also had eight of the top 10 comedies, lead by "Big Bang Theory", the revamped "Two and A Half Men" and "Rob", which also plays well with the 18-49 crowd.

CBS said it was also No.1 online and across social media.

CBS is owned by CBS Corp, Fox is a unit of News Corp, ABC is part of the Walt Disney Co. and NBC is majority-owned by Comcast Corp.

(Reporting By Jill Serjeant; Editing by Bob Tourtellotte)