In a way, last week may have signaled a changing of the guard at the top of the weekly Nielsen ratings list.

No, NBC didn't lose. The Peacock Network is No. 1 for the 38th consecutive week, which means it's closing in on the all-time record for consecutive ratings wins - 40, which CBS set back in the 1962-63 season when it was still the Tiffany Network.But the week's No. 1 show was ABC's "Roseanne," which is single-handedly turning ABC's Tuesday night line-up into the same kind of monster night NBC's Thursday prime time has been since "The Cosby Show" began anchoring the evening. "Roseanne" even out-drew "Cosby" during a week that featured a first-run Huxtable adventure, and ABC's Tuesday night had higher ratings than did NBC's Thursday night - the first time that's happened since the Cosby phenomenon began in 1984.

So strong was "Roseanne's" performance that it turned the show that followed it, the premiere of ABC's "Anything But Love," into a solid top 10 performer. And "Coach," which was in the top 10 last week when it followed "Roseanne" on the schedule, dropped all the way to 38th in its new Wednesday slot.

In fact, all four of ABC's Tuesday night comedies - "The Wonder Years" and "Who's The Boss?" included - finished in the top 10 last week. And if that doesn't remind you of the kind of impact "Cosby" had for NBC on Thursdays, you've probably been hanging out with John Tower too much.

For the record, the top 10 programs for the week were: 1. Roseanne (ABC); 2. The Cosby Show (NBC); 3. Monday Movie: Those She Left Behind (NBC); 4. 60 Minutes (CBS); 5. Who's The Boss? (ABC); 6. Different World (NBC); 7. Anything But Love (ABC); 8. The Wonder Years (ABC); 9. Cheers (NBC); and 10. Murder, She Wrote (CBS).

The week's big losers (not counting Fox and Eastern Airlines) were: 69. Dolphin Cove (CBS) and Tour of Duty (CBS); 71. Movie of the Week: Intrigue (CBS); 72. HeartBeat (ABC); 73. Great Circuses of the World (ABC); 74. Murphy's Law (ABC); and 75. TV 101 (CBS).

- CARROLL O'CONNOR, who underwent emergency heart bypass surgery last weekend, is recovering nicely, according to his physicians in Atlanta. And so is "In the Heat of the Night," his NBC series that had completed filming of all but four of this season's 22 episodes at the time of the operation. NBC has announced that Joe Don Baker ("Walking Tall," "Eischeid") will fill in for O'Connor in those four episodes, playing a sheriff who, appropriately, fills in for Chief Gillespie while he's representing the state of Mississippi at a seminar on domestic terrorism.

- CIRCLE THIS DATE on your calendars: June 30. That's the day when the Screen Actors Guild contract with film and television producers expires. That's also the day a SAG strike could be called if a new contract isn't agreed upon. And if we have to go through another strike-plagued television season I'm going to start up a Utah chapter of Couch Potatoes Anonymous.

- HAVE YOU SEEN Ch. 14's billboard on South Temple? It's my favorite. I mean, how often do you see a picture of Casper the Friendly Ghost with the words "This is real" written under it?

- VIDBITS: Susan St. James has announced that she won't be back for another season on Kate & Allie even if CBS wants to renew the series for a seventh year (which it probably wouldn't want to do anyway, judging by the "Kate & Allie" numbers) . . . While he's in Hollywood for the Academy Awards, Oscar-nominee John Cleese will tape an episode of Cheers in which he will reprise his role as snooty British psychiatrist Simon Finch-Royce . . .