Comcast Corp., which is facing an enforcement action by the Federal Communication Commission over how it treats Internet traffic, will experiment with a new method of managing that traffic to thousands of customers in Chambersburg, Pa., and Warrenton, Va.

The "overwhelming majority" of customers in the two towns will see no difference in their Internet experience during the test, said company spokesman Charles Douglas. The tests will begin tomorrow and run for 30 days.

Comcast, with 14 million residential high-speed Internet customers, expects to test the new method in Colorado Springs, Colo., this summer and to implement it throughout the Comcast system by the end of the year.

FCC Chairman Kevin Martin has said he would make a decision this month on an enforcement action over whether Comcast improperly interfered with Internet traffic. The company faces a potentially huge fine.

Internet advocates and Silicon Valley companies have criticized Comcast for targeting peer-to-peer Internet traffic and not telling its customers. Some consider online streaming through peer-to-peer file-sharing technology, like that of BitTorrent Inc., a future competitor to Comcast's pay-TV business.

With the new method, Comcast said it would not target file-sharing, but would focus on individual heavy Internet users - no matter what they are doing.

The new Internet traffic method will put the online traffic of ordinary Internet users ahead of heavy users at certain times to maintain overall Internet speeds, Douglas said. Thus, the Internet experience for heavy users - so-called Internet hogs - could slow during periods of Internet congestion.

Comcast would be experimenting in the three towns with different vendors supplying this "protocol-agnostic" Internet-management software, he said.