Federal Communications Commission Chairman Kevin Martin said today that the F.C.C. is "ready, willing and able" to punish Comcast Corp. and other network providers that violate commission rules calling for unfettered access to all legal internet content, applications, and services.

The warning from Martin, a Republican, came at a spirited hearing at Harvard Law School, where representatives from Comcast and Verizon Wireless squared off against consumer advocates and academics over the idea of cable and telephone companies can choose to block or slow down the delivery of certain Web content over their wires.

The hearing was held to address complaints leveled by the consumer rights group Free Press, web video company Vuze, and others, charging that Comcast is trying to stifle competition by blocking rival video-on-demand services.

After months of denying the charge that it blocked peer-to-peer file-sharing services such as BitTorrent, Comcast recently conceded it "delays" some peer-to-peer uploads, calling such action "reasonable network management" to ease congestion on its network.

In his testimony, Vuze C.E.O. Gilles BianRosa said that Comcast's actions were anticompetitive and designed to hamper his company.

"We compete with Comcast with delivery of content over the internet," BianRosa said. "What we have here is a horse race, and in this contest Comcast owns the race track — in fact, the only track in town. They also own a horse. We are being told they are only slowing down our horse by a few seconds."

Comcast executive vice president David L. Cohen said his company is merely taking necessary steps to ensure that its network works for all of its customers.

"Don't listen to the rhetoric," Cohen said. "Every network must be managed or no network would function. Peer-to-peer services, during a time of network congestion, create a degradation of our service to our other customers, which is a violation of our acceptable terms of use."

Much of the session was dedicated to defining just what "reasonable network management" means.

"Whatever we think reasonable network management is, it should not include blocking legal services," said Columbia law professor Timothy Wu. He warned that in the absence of safeguards, "the technology of censorship is being built into the system."

Wu said that the issue of "net neutrality" has ramifications for American foreign policy.

"We don't want America to become a place that has a reputation for having a closed or filtered internet," Wu said. "We should be a role model for what an open internet looks like. What happens here will be followed everywhere."

In his opening remarks, Representative Edward J. Markey, a Massachusetts Democrat who chairs the House Subcommittee on Telecommunications and the Internet, disputed the idea that network providers "own" the bandwidth that carries Web traffic.

"The internet is as much mine and yours as it is AT&T's, Verizon's and Comcast's," Markey said, adding that the network operators should not be allowed to "turn BitTorrent into bit trickle."

Last week, Markey and another congressman, Charles W. "Chip" Pickering, a Mississippi Republican, introduced a bill to guarantee net neutrality, The bill would compel the F.C.C. to crack down on network providers who block or discriminate against applications on their networks.

by Sam Gustin