Christine Varney, head of the Justice Department's antitrust division, and Julius Genachowski, chairman of the Federal Communications Commission, said their agencies will examine the transaction closely to ensure the deal does not stifle competition or harm consumers.

Varney and Genachowski made their comments at a Senate Commerce Committee hearing Thursday.

Comcast, the nation's largest cable company, is seeking approval to acquire a 51 percent stake in NBC Universal from General Electric Co. The Justice Department and the FCC are expected to approve the combination with conditions attached. But the review could last at least all year.

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