When General Electric Co sells its control of NBC Universal to Comcast Corp, it will begin an exit from a relationship formed at the dawn of television.

From its birth in 1926, NBC was the first big U.S. radio broadcast network. Since then, it proved itself to be a radio and TV pioneer that somersaulted over rivals with firsts in technology, ratings and entertainment.

Over that time, NBC served as home to some of the biggest names in news and sports, comedy and drama: Milton Berle, Johnny Carson, John Belushi, Tom Brokaw, Chet Huntley and David Brinkley, Jane Pauley, Michael J. Fox and Jennifer Aniston.

Because it was the first network to emerge, it really saw itself as sort of the equivalent of the BBC in Britain, said Michele Hilmes, a media professor at the University of Wisconsin-Madison, and editor of NBC: America's Network.

GE was there at the beginning. It owned 30 percent of the National Broadcasting Company when the Radio Corporation of America launched the network. GE sold its stake in 1932, and 54 years later bought it back along with RCA.

NBC, with its peacock logo developed in 1956 and made permanent in 1979, has coasted at times on its successes and sacrificed advantages.

After dominating the airwaves in the 1980s and 1990s with mega-hits like Cheers, Friends and Frasier, for example, NBC's ratings plummeted in this decade.

As audiences shrank, and GE found itself under pressure from shareholders, NBC changed how it approached the business.

It has concentrated on profit margins and lower costs, particularly for pilot episodes and development. This year it handed its 10 p.m. hour to The Jay Leno Show, a comedy-variety program that costs millions less to produce than the award-winning dramas that have long been NBC's pride.

NBC is not alone -- other networks have leaned toward cheaper shows instead of pricier, often smarter, programming.

Still, its shift is noteworthy. In recent decades, NBC produced a cherished hall of famers, including late programming chief Brandon Tartikoff in the 1980s, who spent time and money on shows and waited longer for them to yield profits, people who worked with the network say.

Now, I feel that the networks are more your boss rather than your partner, said Tom Werner, one of the executive producers of the 1980's blockbuster hit The Cosby Show.

Tartikoff and others like him would nurture a show if they believed in it, said Howard West, one of the executive producers behind another NBC triumph, Seinfeld. No more nurturing now. It's three bumpy ratings and you're gone.

How things may change under Comcast is unclear, but one thing is certain: It would not be GE's problem for much longer. Under the deal, the cable operator would control 51 percent of NBC, setting up a way for GE to gradually depart over seven years. [nN03267923]

NBC, IN BLACK & WHITE

David Sarnoff, the Russian immigrant who built the Radio Corporation of America into a communications empire, formed NBC in 1926 at a pivot point between two eras.

The jazz age was at its height. Stocks were soaring, with the big crash still three years away. French Impressionist painter Claude Monet died. Rock n' roll pioneer Chuck Berry and Cuban revolutionary Fidel Castro were born.

Ownership rested between RCA, GE and Westinghouse, and in the early days the broadcaster had the field to itself. That gave NBC the lead until CBS and its mercurial founder Bill Paley methodically ate Sarnoff's lunch in the 1940s by luring away stars like comedian Jack Benny with big pay raises.

CBS bested NBC in the early 1950s as they shifted to TV, and became the first U.S. network to show color broadcasts. NBC had to content itself with a more nuanced distinction: being the first with a coast-to-coast color broadcast.

NBC clawed its way back over the years with shows that owed much to the programming chieftains who made gutsy entertainment and news choices. But every time they rose on a Little House on the Prairie or Hill Street Blues, along came a career killer like Supertrain or Hello, Larry.

It tends to take the safe middle ground until all of a sudden it looks like it's losing, Hilmes said. Then they rally and hire a bunch of really good people.

In other ways, NBC set the pace for programs that other networks have not been able to beat, such as Saturday Night Live and the morning show Today.

NBC is now part of NBC Universal, thanks to a 2004 deal that gave France's Vivendi SA a 20 percent stake. Many analysts and media executives say it no longer is a good fit for majority owner GE.

Along with the broadcast network, movie studio and theme parks, NBC Universal owns successful cable channels, including business news network CNBC, Spanish-language channel Telemundo, Bravo and the USA Network.

Those deliver most of NBC Universal's revenue, and may work better with Comcast's cable channels. Going to Comcast might determine that a company that distributes TV shows could be open to new ideas about entertainment. Or it could be a flop.

In TV shows, that is what they call the cliffhanger.

 (Reporting by Robert MacMillan, editing by Paul Thomasch and Maureen Bavdek)