For the first time since the mid-1980s, CBS has won one of the all-important sweeps periods.

For the February sweeps, which concluded Wednesday, CBS was first in the A.C. Nielsen numbers with a 13.5 rating and a 22 share, followed by NBC with a 12.9/21, ABC with a 12.1/19 and Fox with a 7.1/11. Arbitron's numbers were nearly the same.It's the network's first win since February 1986, when CBS tied NBC, and its first outright victory since February 1985.

To give you some idea of what a big win this was for the Big Eye, a few months ago the network was given about the same chance of winning a sweeps as Iraq was given of beating the United States.

Oh, the other networks - longtime leader NBC in particular - are trying to downplay the significance of CBS' win. (NBC's major point is that CBS aired considerably more special programming than the other networks.) But even that whining can't take away the deserved glow of the victory.

"The February results are just an indicator of the change in the prime-time race," said David Poltrack, CBS' senior vice president of research. "This is a long-term shift in network trends. We are confident that the best is yet to come."

At the very least, this sweeps period - indeed this season - indicates that NBC's nearly six-season era of dominance is over. The Big Three networks are in a virtual dead heat so far this season.

And Poltrack even disputes NBC claims about special programming. "For the balance of the season, while CBS is gaining momentum in its core schedule, NBC and ABC's declines are accelerating," he said.

For the first quarter of 1991, CBS' overall ratings are up 6 percent over last season. ABC is down 6 percent and NBC dropped 12 percent.

Counting just regular series, NBC edged out CBS by a tenth of a rating point. But while CBS shows an 8 percent improvement, NBC showed a 13 percent decline. (ABC dropped 5 percent.

If nothing else, maybe it's about time TV critics stopped writing about "struggling CBS" or "last-place CBS" or "cellar-dwelling CBS."

Here's a look at the February sweeps' most popular shows:

REGULAR SERIES: 1. "Cheers," NBC; 2. "60 Minutes," CBS; 3. "CBS Sunday Night Movie"; 4. "Roseanne," ABC; 5. "Murphy Brown," CBS; 6. (tie) "Full House" and "America's Funniest Home Videos," both ABC; 8. (tie) "A Different World," NBC and "Designing Women," CBS; 10. "Family Matters," ABC.

SPECIALS: 1. "Very Best of Ed Sullivan," CBS; 2. "The Grammy Awards," CBS; 3. "The Barbara Walters Special," ABC.

MADE-FOR-TV MOVIES: 1. "Sarah, Plain and Tall," CBS; 2. "Lucy & Desi: Before the Laughter," CBS; 3. "The Marla Hanson Story," ABC.

THEATRICAL MOVIES: 1. "Big," ABC; 2. "Good Morning Vietnam," NBC; 3. "The Dead Pool," ABC.

MINISERIES: 1. "And the Sea Will Tell," CBS; 2. "Love, Lies and Murder," NBC; 3. "Son of the Morning Star," ABC.