PHILADELPHIA, PA — A Federal Communications Commission inquiry into its traffic-management practices hasn’t stopped Comcast from forging ahead with efforts to expand its communications empire. The company and Time Warner Cable — from which Comcast purchased a number of local cable service providers and ISPs last year — reportedly are in talks about investing in a wireless company that would give them the WiMax muscle to challenge wireless-market leaders Verizon Communications and AT&T.An anonymous source told the Washington Post that the new WiMax service would be operated by Sprint Nextel and Clearwire. Comcast reportedly is considering investing $1 billion, and Time Warner may contribute as much as $500 million to the joint venture, which would be designed to span the U.S. with next-generation, high-speed wireless service for mobile devices including phones and portable computers.

Sprint and Clearwire have been trying to raise $3 billion to build a nationwide, next-gen WiMax network. Some analysts see WiMax as Sprint’s best hope for the future. The wireless carrier has struggled after losing 1 million subscribers to competitors over the past year.

Communications companies of all stripes are engaged in a race to become the dominant players in the converging markets of telecommunications, television and internet service, according to Jupiter Research. AT&T partnered with Dish Network to add satellite television service to its communications offerings that already included landline and wireless phones and high-speed internet connections. More recently, Verizon partnered with Comcast and Time Warner to offer subscription television.

According to the Post’s anonymous source, Intel and Google also are involved in the Comcast-Time Warner-Sprint Nextel-Clearwire negotiations.