LOS ANGELES — AT&T on Sunday agreed to buy satellite TV provider DirecTV for $48.5 billion, or $95 per share, a deal both companies described as transformational as they seek to take on cable companies and online video providers, delivering content to multiple screens — on living room TVs, PCs, tablets and mobile phones.

With 5.7 million U-verse TV customers and 20.3 million DirecTV customers in the U.S., the combined AT&T-DirecTV would serve 26 million. That would make it the second-largest pay TV operator behind a combined Comcast-Time Warner Cable, which would serve 30 million under a $45 billion merger proposed in February.

“What it does is it gives us the pieces to fulfill a vision we’ve had for a couple of years — the ability to take premium content and deliver it across multiple points: your smartphone, tablet, television or laptop,” AT&T’s Chairman and CEO Randall Stephenson said Sunday.

The companies are aiming to eke out $1.6 billion in annual cost savings in an increasingly expensive and maturing pay TV business. The extra cash flow gives AT&T more ability to invest in its landline and mobile networks for broader reach and faster speeds in a market where it risks falling behind a bulked up Comcast-Time Warner Cable.

The companies promised consumer benefits like more economical bundles that tie mobile phone, pay TV and Internet service together on a single bill.

But the deal could face unique regulatory scrutiny from the Federal Communications Commission and Department of Justice. Unlike the cable company tie-up, the AT&T-DirecTV merger would effectively cut the number of video providers from four to three for about 25 percent of U.S. households. That’s a situation that could result in higher prices for consumers.

Stephenson said those concerns would be addressed with what he called “unprecedented” commitments. Among them:

n DirecTV would continue to be offered as a stand-alone service for three years after the deal’s closing.

n AT&T would offer stand-alone broadband service for at least three years after closing, so consumers could consume video from Netflix and other online services, with download speeds of at least 6 megabits per second where feasible.

n AT&T would expand high-speed broadband access to 15 million more homes — beyond the 70 million that could now get service — within four years.

n AT&T vowed to abide by the open Internet order from 2010 that the Federal Communications Commission is now in the process of revising after a court struck it down.