Comcast Corp. plans to slow Internet service to its heaviest users during periods of congestion, after regulators ordered the company to devise a new method for managing its Web traffic.

The top Internet speeds for targeted customers will be reduced for periods lasting 10 minutes to 20 minutes, keeping service to other users flowing, Mitch Bowling, Comcast's senior vice president and general manager of online services, said.

The Federal Communications Commission found Aug. 1 that Comcast had improperly blocked peer-to-peer programs such as BitTorrent that are used to share videos and other files.

In an order posted on its Web site, the FCC gave the Philadelphia-based company 30 days to provide details of its "unreasonable network management practices" and show how they would be changed by year-end.

"We're going to really have to see all the detail and have all the information," Marvin Ammori, general counsel for the nonprofit group Free Press, said.

Free Press, which promotes universal access to communications, and another organization, Public Knowledge, filed the complaint that resulted in the FCC censure.

The new system will move away from a focus on specific applications that hog Web traffic, Bowling said. Comcast will determine "in nearly real time" whether congestion is caused by a heavy user, he said.

"If in fact a person is generating enough packets that they're the ones creating that situation, we will manage that consumer for the overall good of all of our consumers," Bowling said.

Managing Traffic Comcast reported 14.4 million Internet users at the end of the second quarter. The shares have gained 17 percent this year.

Free Press and Public Knowledge told the FCC that Comcast "is secretly degrading innovative protocols used for transporting and sharing large files, like high-quality television programming and movies."

The FCC acted "to protect consumers' access to the Internet," FCC Chairman Kevin Martin sais.