WASHINGTON — For many TV viewers, the only reason to keep paying for expensive cable subscriptions is to watch sports. And for that, they invariably need ESPN, the powerful network that has exclusive rights to many of the country’s most popular football and basketball games.

Now, that linchpin is being removed. For the first time, sports fans can watch ESPN’s programming streamed online to their tablets, laptops, smartphones and TVs – all without paying a cable or satellite bill.

For $20 a month, viewers will also be able to watch CNN, the Food Network and the Cartoon Network through a new streaming service called Sling TV. Satellite TV provider Dish Network, which is launching Sling, said the service will debut sometime this month.

With Monday’s announcement, 2015 is shaping up to be the year when consumers have more reasons than ever to abandon the expensive bundles of cable channels offered by companies such as Comcast and Verizon.

HBO and Showtime are planning to roll out their own digital streaming services early this year. Sony Entertainment Network will also offer online viewing of channels such as Viacom’s MTV, Nickelodeon and Comedy Central. Millions are already used to paying for Netflix and Hulu Plus.

But ESPN’s entry into online streaming is different. The tremendous demand for the sports channel is unparalleled in the cable TV world. The top 10 most-viewed programs in cable television history are all ESPN programs. And with more people watching TV shows online according to their own schedules, live sports are one of the few things on TV that bring families together to watch in real-time.

On New Year’s Day, the biggest cable audience ever tuned in to ESPN’s new college football playoffs, with 28.2 million viewers watching the Rose Bowl game between Oregon and Florida State, and another 28.3 million catching the Sugar Bowl game between Ohio State and Alabama. On Saturday, the NFL wild-card game between the Arizona Cardinals and the Carolina Panthers became the eighth-most-watched cable program ever, drawing 21.7 milion viewers.

The shift to digital is a high-risk bet for the television industry, which has been dependent on one lucrative model for decades. Companies like Disney-owned ESPN charge cable and satellite companies a certain amount per customer for their programming. The cable and satellite companies, in turn, charge consumers an average of $95.73 per month, according to media research firm SNL Kagan.

Subscriptions to Hulu Plus, Netflix and Sling TV are less than half that amount, although they could also quickly add up.

If too many consumers abandon their Dish Network subscriptions in favor of Sling, the satellite company could lose too much from its core business.

“This is a game-changer for the industry because Dish has to be sure it doesn’t cannibalize its existing customer base,” said Chris Young, an analyst at SNL Kagan. “ESPN is a must-have on the basic-cable platform, and the big question is if $20 is the right point for consumers to push back on cable.”

Some cable networks such as Fox News and AMC have not indicated plans for a stand-alone streaming service. By waiting out the shift, they could risk being left behind, if consumers think their presence isn’t enough to justify a big cable bill.

Dish Network says its market studies show that the most interest in Sling TV will come from millennials who have never subscribed to cable or satellite TV and probably never will. To appeal to these consumers, Dish won’t require contracts, credit checks or installation fees.

But to prevent families from cutting their satellite television subscriptions, Dish said the online service will play on only one device at a time. In other words, if you want to watch ESPN on your phone and tablet, you’ll have to pay $40 per month.