The Justice Department's antitrust division is also looking at the two deals, which critics oppose because they would mean that companies that are rivals in some businesses, like cable and Internet, would become allies in the wireless business.

Verizon Wireless said on December 2 that it would pay Comcast Corp and Time Warner Cable Inc $3.6 billion in a spectrum/marketing deal. A similar deal with privately held cable operator Cox Communications, worth $315 million, was announced in mid-December.

Some rivals such as Sprint Nextel have argued that any review of the spectrum sale by regulators should include other elements of the companies' agreements.

The hearing by the Senate Judiciary Committee's antitrust subcommittee will likely be in March, a committee staffer said. A witness list was not available.

"The subcommittee carefully examines questions about competition in the wireless and video markets, with the ultimate goal of protecting consumers and reducing their cable and cellphone bills, and these deals are no exception," Senator Herb Kohl, the subcommittee's chair, said in a statement.

Verizon Wireless and AT&T, the No. 1 and No. 2 U.S. mobile providers, have said they need more spectrum to support increased consumer demand for videos and other services that soak up bandwidth.

Verizon Wireless is owned by Verizon Communications Inc and Vodafone Group Plc.

Verizon, Comcast and Time Warner declined comment.

(Reporting By Diane Bartz in Washington, D.C.; Additional reporting by Sinead Carew in New York)

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