They're singing a familiar refrain around CBS these days: "Where have all the viewers gone?"

First it was the prime time soap operas. Then they started wondering about the network's prime time line-up in general. Then it was "The CBS Evening News with Dan Rather," which went from No. 1 to battling to stay out of third place faster than you can say "Courage."And now the last bastion of CBS superiority - Sunday nights - is showing signs of weakening, thanks to the home video camera and some crudely drawn animation on the not-so-fledgling-anymore Fox Network.

"America's Funniest Home Videos," the surprise hit of the 1989-90 television season, drew its largest audience ever last week and took over the top spot in the A.C. Nielsen Co. ratings, according to numbers released Tuesday. In doing so it knocked perennial CBS powerhouse "Murder, She Wrote" clear out of the top 20.

That's the good news for ABC. The bad news is that no matter how strong "America's Funniest Home Videos" gets, it can't seem to help "Elvis," the show that follows it on Sunday nights and couldn't even crack the top 40 last week. Nor are viewers heading back to CBS for the last half-hour of "Murder, She Wrote." Rather, they are channel-hopping all the way over to Fox for "The Simpsons," which made its first top 20 appearance last week.

In other words, "America's Funniest Home Videos" isn't helping ABC as much as it's hurting CBS. Well, OK - it's helping ABC a little. I mean, the alphabet network did edge out CBS for second place in the overall ratings, didn't it?

The top 10 programs for the week were: 1. America's Funniest Home Videos (ABC); 2. Cheers (NBC); 3. Roseanne (ABC); 4. The Cosby Show (NBC); 5. A Different World (NBC); 6. 60 Minutes (CBS); 7. The Wonder Years (ABC); 8. Golden Girls (NBC); 9. In the Heat of the Night (NBC); and 10. Who's the Boss? (ABC).

The second 10 consisted of: 11. Empty Nest (NBC); 12. Coach (ABC); 13. Sunday Night Movie: Perry Mason - The Case of the Desperate Deception (NBC), Grand (NBC) and Unsolved Mysteries (NBC); 16. Monday Night Movie: A Son's Promise (ABC); 17. Murphy Brown (CBS); 18. Full House (ABC); 19. Matlock (NBC): and 20. The Simpsons (Fox).

The week's big losers (not counting Fox and the Jazz's home court winning streak) were: 71. Saturday Night With Connie Chung (CBS), H.E.L.P. (ABC), The Bradys (CBS) and Magical World of Disney (NBC); 75. Island Son (CBS); and 77. Grand Slam (CBS).

-NCAA UPDATE: OK, I think we've got everything set for tonight's KSL telecast schedule. With tickets remaining for tonight's NCAA Tournament games at the University of Utah's Huntsman Center, KSL is not going to be able to air CBS's national coverage of the Ohio State-Providence game at 11:05 as scheduled. Nor are they going to be allowed by the network to repeat this morning's BYU-Clemson game, despite the best efforts and arguments of programmer David R. Manookin. But they are going to be able to carry the CBS game at 11:35 p.m. - exciting news only to those teams and their in-town fans, who will be able to see most of the game after returning to their hotels.

Anyway, KSL will pre-empt "The Pat Sajak Show" tonight (I know, I know, but you'll survive) and fill time until 11:35 with both episodes of a "M*A*S*H" two-parter at 10:35 and 11:05 p.m.

-KTVX IS EXPANDING its news programming next month when it adds a 5:30 p.m. local newscast to its Saturday and Sunday schedules. Weekend anchors Kim Johnson and Jon DuPre will handle both 5:30 and 10 p.m. newscasts, with one new reporter - Deseret News reporter Rob Rice - being added to the two who are currently covering the weekend beats for Ch. 4. The new newscast will begin April 7.