By Lisa Richwine and Jessica Toonkel

(Reuters) - U.S. TV networks, buoyed by strong demand from advertisers, are adding hours of coverage for this week's Republican National Convention compared to four years ago and planning to use social media to capture any unexpected moments, executives said.

Presumptive presidential nominee Donald Trump may be new to politics. But the former star of his own reality show "The Apprentice" is a TV veteran who has promised to throw out the traditional convention script and provide a "showbiz" feel. Adding to the programing uncertainty are protests outside the convention hall in Cleveland and the possibility of dissent among delegates.

"It's safe to say that there are going to be surprises," said Sam Feist, Washington bureau chief for CNN, the cable news network owned by Time Warner Inc .

The stakes are high for broadcast and cable networks. Media analysts predict viewership for Trump's acceptance speech could surpass the record 38 million who watched Barack Obama address the Democratic convention in 2008.

The potential for the unexpected at what is usually a meticulously staged event is driving strong advertiser demand, network executives said. CNN is pulling in between $40,000 and $100,000 for 30-second spots, a source familiar with the matter said. That is far above the typical cost of roughly $7,000 for a primetime ad on CNN.

"We are 100 percent sold on primetime and about 95 percent sold on other slots," said Katrina Cukaj, executive vice president of portfolio sales and client partnerships at CNN parent Turner Broadcasting. She declined to comment on rates.

Quick service restaurants and movie studios are running more spots than in past conventions, Cukaj said. "The advertisers are a lot more diverse than I have ever seen," Cukaj said.

Broadcaster CBS has seen strong ad sales for both conventions and has booked ads from the entertainment, packaged goods, travel and other industries, a network source said.

In 2012, TV advertisers spent $5.8 million during both conventions, compared to $7.8 million in 2008, according to Kantar Media.

Cable networks will provide coverage throughout each day and into the evening. Broadcast networks plan one hour of primetime coverage each of the four nights, plus online reports. In 2012, broadcasters aired an hour of only the last three nights.

CNN will have hundreds of staff on the ground, more than any previous convention, Feist said. For the first time, the channel is anchoring every show from Cleveland through noon Friday.

The network will face plenty of competition. Fox News Channel, owned by 21st Century Fox , began its coverage from Cleveland on Thursday, four days before the start, compared to Sunday in years past. It also added staff outside to cover protests.

Trump's acceptance speech could attract more than 40 million viewers, said Kyle Roberts, president and chief executive of Smart Media Group, a media buyer that works with Republican candidates.

Some brands will avoid the convention, said Barry Lowenthal, president of The Media Kitchen, a media buyer.

"It's just dangerous territory," Lowenthal said. "It's very unpredictable content. I'm not sure that convention is going to enhance any brand's image. Why go there if you can go elsewhere?"

Media outlets say they will rely more heavily this year on social media and live streams.

MSNBC correspondent Jacob Soboroff said he expects to broadcast live most of the week. When not on television, he plans to be on Snapchat, Twitter and possibly Facebook Live.

"This is going to be a different kind of convention," Soboroff said. "It doesn't feel like business as usual because there is a lot of energy around that feels uncertain."

Walt Disney Co's ABC News will run up to six live streams simultaneously on its website and apps. Live coverage from CBS will appear on Twitter and the 24-hour CBSN mobile app.

CBS is preparing for the possibility that Trump will appear in some role every night, another break from tradition, CBS News President David Rhodes said.

(Reporting by Lisa Richwine in Los Angeles and Jessica Toonkel in New York; Editing by Sue Horton and Lisa Girion)