Comcast Corp. will buy AT&T's Denver-based broadband unit, winning a bidding contest to acquire the largest U.S. cable television operator, a source close to the deal said Tuesday night.

AT&T's selection of Comcast came five months after it spurned a $41 million unsolicited bid by the nation's No. 3 cable operator for the cable division.

The source, who spoke on condition of anonymity, said the deal is valued at about $70 billion, including about $22 billion in AT&T debt.

Further financial details were expected to be released in a formal announcement Wednesday night, the source said.

An AT&T spokeswoman did not immediately return a phone message seeking comment.

The company's board met earlier this month to discuss bids for its broadband operations — including the possibility of spinning it off as a standalone business — but decided to have further discussions with bidders before making a decision.

Other companies that submitted bids for AT&T Broadband were AOL Time Warner Inc. and Cox Communications Inc.

Microsoft Corp. also considered increasing its stake in AT&T Broadband, or participating in a bid by Comcast or Cox in return for a stake.

AT&T broadband has about 13.8 million cable subscribers, including more than 3 million who use its digital video services, according to the National Cable Television Association.

The bidding process started after Comcast, the nation's No. 3 cable operator, made a $41 billion hostile bid in July for AT&T Broadband.

Comcast's surprise offer came the day before the New York-based AT&T's spinoff of its wireless operation into an independent company, the first stage in a plan to break the communications conglomerate into five separate companies.

The biggest of those AT&T units is the sprawling cable operation that AT&T cobbled together with a $100 billion acquisition spree that began three years ago.