KTTV wins ratings derby.

When Fox Broadcasting Co. debuted 10 years ago on KTTV-Channel 11, some observers predicted it would be a matter of decades, if ever, before the station would become a serious challenger to the Big Three networks.

So much for predictions.

Channel 11, once known more for "I Love Lucy" reruns than ratings, is now L.A.'s most watched station on week-nights - a first in its 48-year history - and the third most popular channel overall.

According to Nielsen Media Research, KTTV beat out L.A.'s seven other VHS, TV stations in all key demographic categories on weeknights during the crucial May sweeps period.

Nielsen conducts four sweeps each year - in February, May, July and November. The May sweeps are by far the most important because TV networks and local stations use their ratings from that period to set advertising rates for the new fall season. As a result, May is when stations air their best and most expensive programming.

KTTV General Manager Diana L. Vargas describes the station's showing during the May sweeps as "huge, absolutely huge."

KTTV, which is run by the Fox Television Stations Group, has long gone after the younger crowd by showcasing risque comedies, popular syndicated programs and sports.

Vargas, who took over as general manager last January, after joining Channel 11 nine years ago, credits the station's surprising popularity to its ability to draw and keep youthful viewers, even as they age.

"We targeted a young audience and that audience has grown up," explains Vargas. "They've stayed with us because we're much broader based."

That move to a broader base is reflected in Fox's expansion from initially airing only youth-oriented programs to its current list of popular shows that include "The X-Files," and "New York Undercover."

KTTV's ratings for the May sweeps period, from sign-on to sign-off, ranked behind only KNBC-TV Channel 4 and KABC-TV Channel 7. KCBS-TV Channel 2 brought up the rear, coming in fourth.

Mitch Stern, president and chief operating officer of Fox Television Stations Group, who oversees Fox's 22 stations nationwide, said the L.A. station is a bellwether for other markets. KTTV is also the highest-rated of Fox's 22 stations.

"When it comes to TV, the L.A. audience is by far the most sophisticated. If you put on something good, they stay. If you put on something bad, they run away," says Stern. "This is Hollywood. You have to satisfy them to a very high degree. ... If it works here we go to New York, Chicago all over the place."

Stern acknowledges that 10 years ago KTTV was nothing to write home about. "It was scary," notes Stern.

KTTV's willingness to take a chance on unconventional comedies like "Married with Children," and "The Simpsons" is what helped the station take off.

"People thought we were idiots when we decided to do 'The Simpsons.'" says Stern. "We put a lot of things in L.A. that no one else would."

The network's first sitcom, "Married with Children," was blasted by critics when it first appeared. The show aired for 11 years, becoming the longest-running sitcom in the history of television.

Other Fox shows such as "Melrose Place" and "Beverly Hills 90210" have also kept a loyal following.

But the KTTV programs drawing the highest number of viewers are reruns.

"Home Improvement," which runs week-nights at 6:00 p.m. and again at 7:00 p.m., outperformed all local news programs as well as other syndicated shows during the May sweeps.

The show tallied a 4 rating, making it the No. 1 program among men and women between the ages of 18 and 54. It posted a whopping 157 percent gain from a year ago among 25-to-54-year-old women.

"The Simpsons," which KTTV airs at 6:30 and again at 7:30 p.m., beat all competing shows in its time slots, and drew 96 percent more adults aged 18 to 49 during the May sweeps than in the year-earlier May sweeps.

KTTV's 10 p.m. local newscast also took the ratings crown.

Overall ratings are important, but especially crucial are ratings among three key demographic categories: Men and women aged 18 to 34. 18 to 49 and 25 to 54. These three categories hold the highest spenders of discretionary income, and therefore, are the most important in terms of drawing advertising dollars.

"Overall when it comes to TV, the classic demographic is 18 to 49," says John Fuller, president of the Fuller Group, an L.A.-based advertising firm. "That age group has the highest discretionary income and tends to buy the most."

Although KTTV executives would not comment on revenue gains, the station's newfound success will clearly bring it more advertising dollars, according to experts.

"Their revenue will likely go up," says Allen Banks, executive vice president of North American media for Saatchi & Saatchi Advertising Worldwide. "There are clearly advertisers who want to be with the winner ... the TV station that gets talked about at the water cooler on Monday morning."

Banks adds that the advertising market is no longer dominated by the Big Three and that ad dollars are being spread out more evenly across several stations.

"What's happening now is, with the four networks, the two smaller networks (UPN and WB) and cable television, it gives advertisers a greater number of places to spend advertising dollars," explains Banks. "KTTV has to be sensible in terms of finding a balance of rating and charges."

Vargas stresses that KTTV has no intention of using its recent ratings jump to gouge advertisers. The the most important thing is grabbing the highest share of the audience, not becoming the top grossing local station, she says.

Meanwhile, executives at rival station KCBS are following Fox's lead by beefing up programming aimed at younger audiences.

"A lot of our new fall network prime is a little more action-oriented. ... Obviously it's in response to the competition," says Rozanne Englehart, KCBS director of research.

Before KTTV's rating success, the Big Three had not had a serious rival in more than three decades.

Vargas predicts KTTV is in for the tong haul and will not be backing down anytime soon.

"The strength and the growth of the station is consistent. This is not a fluke," she insists.