By Malathi Nayak

NEW YORK (Reuters) - Comcast Corp <CMCSA.O> on Wednesday posted higher third-quarter revenue and profit, benefiting from its NBCUniversal unit's broadcast of the Rio Olympics and the addition of new video customers.

Cable and satellite TV companies have been threatened by lower-priced offerings from streaming video services, such as Netflix Inc <NFLX.O>. In response, Comcast has been expanding its internet business and investing in media assets, including "Kung Fu Panda" producer DreamWorks Animation.

Investors will keep a close watch on whether Comcast, the largest U.S. cable and high-speed internet provider, could face new competition from AT&T Inc's <T.N> proposed $85.4 billion acquisition of Time Warner Inc <TWX.N>.

If regulators approve that deal, AT&T would own a national wireless network, while Comcast does not, MoffettNathanson analyst Craig Moffett said in a note. "So what's it gonna be, Comcast? Your move."

Asked about the AT&T deal on a conference call, Comcast Chief Executive Officer Brian Roberts declined to comment.

"The (Comcast-NBCUniversal) assets are great," he said. "They are working well together, adding customers, adding new products and real market leadership in almost every area."

Wall Street is also tracking Comcast's plans to introduce a wireless service in mid-2017. Comcast struck a 2011 deal with Verizon Communications Inc <VZ.N> to resell the wireless provider's cellular service in exchange for airwaves.

Comcast said revenue rose 14.2 percent to $21.32 billion in the quarter from a year earlier. Analysts on average had forecast $21.16 billion, according to Thomson Reuters I/B/E/S.

Revenue from NBCUniversal, which includes the NBC television network and Universal film studio, increased 28.3 percent to $9.18 billion, helped by the Olympics and its Harry Potter theme park attractions.

Net income attributable to Comcast rose 12.1 percent to $2.24 billion. Excluding special items, earnings of 92 cents per share beat the analysts' average estimate by a penny.

Comcast shares closed 3 percent lower at $62.56.

Philadelphia-based Comcast added 32,000 video subscribers during the quarter, compared with a year-earlier loss of 48,000.

To keep its pay-TV subscribers, Comcast has been enhancing its X1 set-top box to let viewers search shows and movies easily, expanding its on-demand library and improving its customer service. Last month, through a beta test, it began letting customers stream Netflix through its X1 service.

Revenue from the high-speed internet business rose 8.8 percent to $3.4 billion in the quarter, while customer additions increased 3.1 percent to 330,000.

Business services revenue increased 15.5 percent to $1.39 billion.

(Reporting by Malathi Nayak; Editing by Bernard Orr and Lisa Von Ahn)