UPN’s thundering "Smackdown" will move in with The WB’s cerebral "The Gilmore Girls" in September, when the rival television networks will shut down and re-emerge as one.

The new network - to be called The CW - will debut on many former affiliates, including KSTW-TV, Seattle’s UPN station. Executives for CBS and Warner Bros. Entertainment said Tuesday that The CW will offer the most popular shows from UPN and The WB - programming largely targeted at the hard-to-reach 18-34 age demographic - including "America’s Next Top Model," "Smallville," "Veronica Mars," "Everybody Hates Chris" and "Reba."

"The CW is going to be a real competitor, a destination for young audiences, diverse audiences, and a real favorite with advertisers," said Leslie Moonves, president and CEO of CBS, which has owned UPN since 2002. "The CW will be able to do something truly remarkable: program already-hit shows every single day of the week, programs that consistently rank No. 1 or No. 2 in their time slots in the most coveted young-adult demographic."

By joining forces, the two small networks, both launched in 1995, essentially are bowing to the reality of an increasingly competitive marketplace, executives acknowledged. The merger marks the first time a commercial broadcast network has disappeared since the money-losing DuMont network went out of business in 1955.

The WB and UPN have lost more than $1 billion each since their inceptions. The WB has turned a profit twice; UPN never has been profitable. Both faced high production costs for original programming but produced few breakout hits. They were viewed widely as fringe channels against the network landscape of the big four: ABC, CBS, NBC and Fox.

But the two upstarts competed vigorously against one another, a rivalry that reached a bitter apex in 2001 when UPN lured the teen cult classic "Buffy the Vampire Slayer" away from The WB. Warner Bros. responded by killing Buffy, played by Sarah Michelle Gellar, in the final episode for its network, forcing a cemetery resurrection for the UPN debut.

During November sweeps, UPN averaged about 3.7 million viewers nightly and The WB about 3.5 million, meaning they were viewed in fewer than 3 percent of U.S. households, both down slightly from a year earlier. By comparison, No. 1 CBS was viewed in more than 9 percent of households on any average night, reaching 14.6 million viewers. Merging the networks

Here are some of the top offerings from each network

CBS and Warner Bros. Entertainment each will own 50 percent of the new venture, which will be carried by Tribune Co. stations and CBS-owned affiliates that carry UPN.

The new venture likely will mean significant job losses, most from Burbank, Calif.-based WB, where 240 people work. And there will be fewer outlets of programming for producers, writers and television studios.

Tribune Broadcasting, a WB stakeholder, signed a 10-year deal to carry The CW on its stations.

"From Tribune’s perspective, this is the best of all worlds," said Dennis FitzSimons, chairman and CEO of Tribune.

The merger will have a ripple effect at local stations, as some looked forward to doubling their programs and others learned they would be giving up their network status.

In the Seattle-Tacoma market, it was a happy day for CBS owned-and-operated UPN affiliate KSTW-TV.

"We are thrilled to be able to align ourselves with The CW, which promises to be a major broadcasting competitor right out of the gate this fall," KSTW general manager Anna Shreve said.

At Tribune-owned KTWB, which will have to surrender its WB lineup to KSTW, the scene was less serene. General manager Pam Pearson said KTWB likely will fill its prime-time hours with syndicated shows for the 2006-07 season.

News of the merger was kept tightly under wraps until Tuesday, when reporters were summoned to a news conference at New York’s St. Regis Hotel.

Barry Meyer, chairman and chief executive officer of Warner Bros. Entertainment, called the new network "a partnership whose time has come."

The CW will copy The WB’s prime-time scheduling approach of airing shows from 8 to 10 p.m. weeknights and 7 to 10 p.m. Sundays and offering no programming on Saturday nights, the weakest viewing night. The new network also will continue a Saturday morning block of children’s shows, now known as "Kids’ WB!"

The CW takes its name from the first initials of each parent company.

"We couldn’t call it The WC for obvious reasons," Moonves quipped. WC is an abbreviation of the British term "water closet," or toilet.

Dawn Ostroff, president of UPN, will serve as entertainment president of The CW, while John Maatta, chief operating officer of The WB, will take on that role at the new network. Bill Morningstar, The WB’s executive vice president of advertising sales, will become head of sales at The CW.

The rest of the senior executive talent will be a blend of executives from UPN and The WB, along with the possibility of some outside hires.