NEW YORK (AP) — If television's weekly list of the most popular programs is starting to get monotonous by the fourth week of the new TV season, that's OK by CBS.

The network was nation's most popular in primetime again last week, with an average of nearly three million more viewers than second-place ABC. "NCIS" and "NCIS: Los Angeles" were the most-watched program and new program for the fourth straight week, the first time a network can claim that at the start of a season since NBC did it with "ER" and "Jesse" in 1998, the Nielsen Co. said.

There are other small stories developing. ABC's "Modern Family" and "Cougar Town" are moderate successes as the network tries to establish a Wednesday comedy night. That same night, ABC's "Hank" (No. 60 last week) is looking like a failure for star Kelsey Grammer. NBC's nurse-centric "Mercy" is faring better than the network's more action-oriented "Trauma."

ABC's "Flash Forward" signs of being a successful science fiction drama on Thursdays. Nielsen said the show's pilot episode was watched more often on computer than any other show on a broadcast Web site in September.

For the week, CBS averaged 11.9 million viewers (7.5 rating, 12 share), and was also most popular among viewers aged 18-to-49. ABC averaged 9 million in primetime (5.8, 10), Fox had 8.1 million (4.8, 8), NBC had 7.4 million (4.7, 8), the CW had 2.3 million (1.5, 2) and Ion Television had 910,000 (0.6, 1).

Among the Spanish-language networks, Univision led with a 3.4 million average in prime-time (1.8 rating, 3 share), Telemundo had 1.1 million (0.6, 1), TeleFutura had 920,000 (0.5, 1) and Azteca had 220,000 (0.1, 0).

NBC's "Nightly News" topped the evening newscasts with an average of 8.8 million viewers (5.7, 11). ABC's "World News" was second with 7.7 million (5.2, 10) and the "CBS Evening News" had 5.9 million viewers (4.1, 8).

A ratings point represents 1,149,000 households, or 1 percent of the nation's estimated 114.9 million TV homes. The share is the percentage of in-use televisions tuned to a given show.

The Top 20
Primetime viewership numbers compiled by the Nielsen Co. for Oct. 12-18. Listings include the week's ranking, with viewership for the week and season-to-date rankings in parentheses. An "X" in parentheses denotes a one-time-only presentation.

1. (1) "NCIS," CBS, 21.04 million viewers.

2. (2) NFL Sunday Night Football: Chicago at Atlanta, NBC, 18.17 million viewers.

3. (4) "Dancing With the Stars," ABC, 16.79 million viewers.

4. (3) "NCIS: Los Angeles," CBS, 15.38 million viewers.

5. (7) "CSI: Crime Scene Investigation," CBS, 15.38 million viewers.

6. (7) "The Mentalist," CBS, 15.08 million viewers.

7. (15) "60 Minutes," CBS, 14.32 million viewers.

8. (12) "Two And a Half Men," CBS, 14.17 million viewers.

9. (19) "Dancing With the Stars Results," ABC, 13.96 million viewers.

10. (9) "Criminal Minds," CBS, 13.92 million viewers.

11. (5) "Grey's Anatomy," ABC, 13.79 million viewers.

12. (12) "Desperate Housewives," ABC, 13.68 million viewers.

13. (6) "House," Fox, 13.5 million viewers.

14. (15) "CSI: New York," CBS, 13.4 million viewers.

15. (12) "CSI: Miami," CBS, 13.27 million viewers.

16. (18) "The Big Bang Theory," CBS, 13.07 million viewers.

17. (15) "The Good Wife," CBS, 12.98 million viewers.

18. (11) "Sunday Night NFL Pre-Kick," NBC, 12.0 million viewers.

19. (20) "Survivor: Samoa," CBS, 11.78 million viewers.

20. (24) "The Amazing Race 15," CBS, 10.92 million viewers.