NEW YORK — For more than 60 years, TV stations have broadcast news, sports and entertainment for free and made their money by showing commercials. That might not work much longer.

The business model is unraveling at ABC, CBS, NBC and Fox and the local stations that carry the networks' programming. Cable TV and the Web have fractured the audience for free TV and siphoned its ad dollars. The recession has squeezed advertising further, forcing broadcasters to accelerate their push for new revenue to pay for programming.

That will play out in living rooms across the country. The changes could mean higher cable or satellite TV bills, as the networks and local stations squeeze more fees from pay-TV providers such as Comcast and DirecTV for the right to show broadcast TV channels. The networks might even ditch free broadcast signals in the next few years. Instead, they could operate as cable channels — a move that could spell the end of free TV as Americans have known it since the 1940s.

"Good programing is expensive," Rupert Murdoch, whose News Corp. owns Fox, told a shareholder meeting this fall. "It can no longer be supported solely by advertising revenues."

Fox is pursuing its strategy in public, warning that its broadcasts — including college football bowl games — could go dark Friday for subscribers of Time Warner Cable, unless Fox receives higher fees. For its part, Time Warner Cable is asking customers whether it should "roll over" or "get tough" in negotiations.

The future of free TV also could be altered as the biggest pay-TV provider, Comcast Corp., prepares to take control of NBC. Comcast has not signaled plans to end NBC's free broadcasts. But Jeff Zucker, who runs NBC and its sister cable channels such as CNBC and Bravo, told investors this month that "the cable model is just superior to the broadcast model."

The traditional broadcast model works like this: CBS, NBC, ABC and Fox distribute shows through a network of local stations. The networks own a few stations in big markets, but most are "affiliates," owned by separate companies.

Traditionally the networks paid affiliates to broadcast their shows, though those fees have shrunk to near nothing as local stations lost viewership. What hasn't changed is where the money mainly comes from: advertising.

Cable channels make most of their money by charging pay-TV providers a monthly fee per subscriber for their programing. On average, the pay-TV providers pay about 26 cents for each channel they carry, according to research firm SNL Kagan. A channel as highly rated as ESPN can get close to $4, while some, such as MTV2, go for just a few pennies.

With both advertising and fees, ESPN has seen its revenue grow to $6.3 billion in 2009 from $1.8 billion a decade ago, according to SNL Kagan estimates. It has been able to bid for premium events networks had traditionally aired, such as football games. Cable channels also have been able to fund high-quality shows, such as AMC's "Mad Men," rather than recycling movies and TV series.

That, plus a growing number of channels, has given cable a bigger share of the ad pie. In 1998, cable channels drew roughly $9.1 billion, or 24 percent of total TV ad spending, according to the Television Bureau of Advertising. By 2008, they were getting $21.6 billion, or 39 percent.

Having two revenue streams — advertising and fees from pay-TV providers — has insulated cable channels from the recession. By contrast, over-the-air stations have been forced to cut staff, and at least two broadcast groups went bankrupt in 2009.

Fox illustrates the trend: Its broadcast operations reported a 54 percent drop in operating income for the quarter that ended in September. Its cable channels, which include Fox News and FX, boosted their operating income 41 percent.

Analyst Tom Love of ZenithOptimedia estimates ad revenue at the big networks dropped 9 percent in 2009 and will be followed by an 8 percent drop in 2010 and zero growth in 2011.

A small chunk of the ad revenue is being recouped online, where the networks sell episodes for a few dollars each. Media economist Jack Myers projects online video advertising will grow into a $2 billion business by 2012, from just $350 million to $400 million in 2009.

But that is not enough to make up for the lost ad revenue on the airwaves.

Advertisers spent $34 billion on broadcast commercials in 2008, down by $2.4 billion from two years earlier, according to the Television Bureau of Advertising.