It's official. ABC's Roseanne is a bona fide, No. 1, don't-look-now-but-here-come-the-clones hit, a fact that was clearly substantiated last week when the ABC sitcom hit the top spot for the first time in the weekly Nielsen ratings.

It marked the first weekly win by a TV rookie this season, and the first timea regularly scheduled ABC program has ranked No. 1 in three years. It also makesit clear that "Roseanne's" success is not predicated upon the holdover audience from its popular lead-in, "Who's The Boss?" Instead, the new show is drawingadditional viewers to ABC, which hasn't had a consistent No. 1 contender since the heyday of "Three's Company" and "Laverne and Shirley" in the late 1970s and early 1980s.The popular success of "Roseanne" means that ABC is closely following the pattern NBC used earlier this decade to move from the ratings cellar into the penthouse:

- Start with some critically acclaimed "quality" series (for NBC it was "Hill Street Blues," "Cheers" and "St. Elsewhere; for ABC it's "thirtysomething" and "The Wonder Years");

- Come up with a big blockbuster that helps you totally dominate one night ("The Cosby Show" did it for NBC on Thursdays; "Roseanne" is doing it for ABC on Tuesdays);

- And then sit back and wait for the network in power to weaken as their hits age (as NBC did with then-No. 1 CBS).

And there was even some good ratings news for CBS. Murphy Brown, the acclaimed new series that started out so slowly, seems to be finding an audience, finishing in the top 20 for the first time.

The top 10 programs for the week were: 1. Roseanne (ABC); 2. The Cosby Show (NBC); 3. Cheers (NBC); 4. Who's the Boss? (ABC); 5. Monday Night Football (ABC); 6. Different World (NBC); 7. L.A. Law (NBC); 8. Matlock (NBC); 9. Night Court (NBC); and 10. Heat of the Night (NBC).

The second 10 consisted of: 11. Dear John (NBC); 12. Bob Hope Special (NBC); 13. Moonlighting (ABC); 14. Growing Pains (ABC); 15. Unsolved Mysteries (NBC); 16. Golden Girls (NBC); 17. Designing Women (CBS); 18. Murphy Brown (CBS); and 19. Empty Nest (NBC), Kate & Allie (CBS) and Head of the Class (ABC).

The week's big losers (not counting Fox and everyone who lost to the Miami Heat last week) were: 64. Saturday Night Movie: The Homecoming (CBS) and TV 101 (CBS); 66. The Life and Adventures of Santa Claus (CBS) and Alice in Wonderland (ABC); and 68. Incredible Sunday (ABC).