Following are the top 20 network primetime shows last week, ranked according to the percentage of the nation's 88.6 million TV households that watched, as measured by the A.C. Nielsen Co. A share represents the percentage of actual sets-in-use tuned to a particular program when it aired. ---Rating------------------------Share--Network 1....32.0...Browns/Broncos Overrun 50...NBC 2....31.7...The Cosby Show........ 47...NBC 3....27.9...Cheers................ 41...NBC 4....27.2...A Different World..... 41...NBC 5....25.9...Night Court........... 39...NBC 6....23.8...The Golden Girls...... 39...NBC 7....23.4...Growing Pains......... 34...ABC 8....22.5...Who's the Boss?....... 33...ABC 9....21.6...L.A. Law.............. 36...NBC 10...20.5...Family Ties........... 30...NBC 11...20.1...Murder, She Wrote..... 29...CBS 12...19.9...Crash Course.......... 32...NBC 13...19.8...ALF................... 29...NBC 14...19.6...NFL Post-Game Show.... 30...NBC 15...19.4...Matlock............... 28...NBC 16...19.0...Amen.................. 32...NBC 17...18.8...My Two Duds........... 27...NBC 18...18.7...Perfect Strangers..... 28...ABC 19...18.6...Valerie's Family...... 27...NBC 20...18.2...Head of the Class..... 27...ABC

NBC scored its 12th win in a row in the Nielsen ratings last week, thanks to football playoffs and another strong showing by its Thursday night lineup. The No. 1 network had an 18.0 rating and a 29 share overall, compared with a 13.7/22 for CBS and a 12.5/20 for ABC.

NBC now has a season-to-date rating of 16.5. CBS is second with 13.6, and ABC third with 13.2.

The Denver-Cleveland game's 47-minute runover into prime time was the top-rated broadcast of the week with a 32.0/49. Football games are included in the rankings if they run 30 minutes or more into prime time.

"The Cosby Show" was second, followed by the rest of NBC's Thursday night comedies. NBC had the top six shows and eight of the top 10.

With ABC's "Dolly" in its new Saturday time slot -- it chalked up an 11.3/19 to finish 62nd for the week -- Sunday night was a battle of made-for-TV movies. NBC won the matchup with "Crash Course," which scored a 19.9/32 to finish 12th for the week. CBS' "Alone in the Neon Jungle" was second with a 17.6/28, and ABC's "Stranger on My Land" pulled an 11.5/18.

"CBS Evening News" stretched its winning streak to 17 weeks in a row, though it was a very tight three-way race last week. CBS had an average rating of 12.5/21, ABC's "World News Tonight" took a 12.0/20, and "NBC Nightly News" was third with an 11.9/20.

The five lowest-rated shows were CBS' "West 57th," in 69th place, followed by ABC's "Ohara," CBS' rerun of "Steve Martin: Comedy Is Not Pretty," ABC's rerun of "Diamonds Are Forever," and "The Charmings" in 73rd and last place.

Captain Airwaves is on vacation. His column will resume when he returns.