The 1990-91 television season is officially over, and NBC won. So how come the Peacock isn't doing much in the way of celebrating?

Well, the win was less than overwhelming. As a matter of fact, the Big Three networks finished in a virtual dead heat.And, overall, it was a dreadful season for NBC - its ratings slid badly and only a huge lead from last season held off ABC and CBS.

NBC averaged a 12.7 rating, ABC a 12.5 and CBS a 12.3. (Each rating point equals 931,000 homes.)

But all three networks averaged a 21 share. (A share is the percentage of homes actually watching television tuned in to a particular network.)

It wasn't a good year for the networks. The Big Three's combined share of the audience fell 3.5 percent to 62.4 percent, the lowest in history.

None of the networks could come up with a really big hit this season, despite airing more than 60 new shows. About the closest any of them could come was "America's Funniest People" and "Fresh Prince of Bel Air," but by season's end "Fresh" was losing more often than not to "Evening Shade."

NBC plummeted 13 percent, ABC fell 3 percent and Fox (which expanded from three to five nights of programming) dropped 2 percent. Only CBS showed any improvement, increasing a modest 2 percent.

Oh, the folks at NBC are trying to put the best face on this disaster. They point out that it was the network's sixth season in a row in first place, that it won four nights of the week and that its regular programming - led by No. 1 "Cheers" - was a clear No. 1 in total households.

But NBC has become the House of Aging Hits. And many of those hits aren't aging well. "The Cosby Show" lost 26 percent of its audience, "Night Court" 21 percent, "The Golden Girls" 18 percent, "L.A. Law" 15 percent, "Unsolved Mysteries" 13 percent and "In the Heat of the Night" 12 percent.

Second-place ABC had a good deal more to celebrate than first-place NBC.

The weekly Nielsens measure the total number of households, a figure the networks use mostly just for bragging rights. What they use to sell ads are demographics - the groups advertisers want to reach.

And looking at demographics, ABC was a clear winner. That network won among adults 18-34, adults 18-49, adults 25-54, women 18-34, women 18-49, women 25-54, men 18-34, men 18-49, men 25-54, teenagers and kids.

All of which means that, despite losing to NBC in total households, ABC can charge more for its commercials. No wonder they're gloomy at NBC.

Seven of ABC's regular series improved on their ratings over 1989-90 - "Anything But Love," "Doogie Howser, M.D.," "Family Matters," "Full House," "Perfect Strangers," "PrimeTime Live" and "20/20."

But all was not well at ABC, as the network's biggest hits took the biggest hits in the numbers - "The Wonder Years" plummeted 26 percent, "Roseanne" dropped 22 percent, "America's Funniest Home Videos" declined 20 percent and "Who's the Boss?" dropped 16 percent.

Meanwhile, over at CBS, there was near euphoria despite the third-place finish. Not only was there improvement in the network's ratings, but for the first time in years the Big Eye was competitive.

CBS finished first in the weekly ratings seven times and second eight times. That's a considerable improvement over zero wins and seven second-places in 1989-90.

Perhaps more importantly, eight of CBS' returning programs increased their audiences this season.

Demographically speaking, CBS tied NBC for first among total adults (up from third last season) was No. 1 in total men (up from third), was No. 1 among adults 35-54 (up from third).

The Big Eye remained No. 1 in daytime programming and moved from third to first on Saturday morning.

And, for the first time since 1986, CBS became the most-watched network over the entire broadcast day.CNN AND THE WAR: The effect of the war in the Persian Gulf on the Cable News Network was dramatic but temporary.

The two weeks before hostilities broke out (Jan. 1-13), CNN averaged a 1.2 rating. That jumped to a 6.3 when the war began, before falling to a 4.1 the following week and a 3.6 a week later.

By the first week of April, CNN's was down to a .7.THE FINAL WEEK: CBS went out on top, winning the last week of the season with a 12.4 ratings, compared to ABC's 11.3 and NBC's 11.0. Last week's top shows were:

1. "Cheers" (NBC); 2. "Different World" (NBC); 3. "60 Minutes" (CBS); 4. "Roseanne" (ABC); 5. CBS Sunday Movie: "Absolute Strangers"; 6. "Designing Women" (CBS); 7. "Murphy Brown" (CBS); 8. "Coach" (ABC); 9. "America's Funniest People" (ABC); 10. "Seinfeld" (NBC).