Facing criticism from a member of Congress and privacy advocacy groups, the Comcast Corporation said today that it would no longer store data that would enable it to track individual subscribers' Internet surfing habits.

Comcast, which provides high- speed Internet access through cable modems to 948,000 customers, said it changed the policy to reassure customers it would not track their individual movements on the Internet. But the company said that even before it changed the policy, it had not tracked individuals' behavior, but rather, had sought to gather aggregate data on the habits of its users.

Internet service providers routinely track aggregate data, without identifying individuals, to find out what sites their users most frequently visit; the providers then store those Web pages so they can be more quickly delivered to users. But privacy advocates expressed concern that the way Comcast was gathering the information left open the possibility that the company could deconstruct the data and create logs of what sites subscribers visited.

Dave Watson, executive vice president for marketing at Comcast, said the company never created individual use logs, nor intended to. "We don't want anyone to be concerned we'd take that next step forward," he said, explaining the company's position to abandon its current tracking policy. "We just want to take this issue off the table."

People close to the company said it was leaving open the possibility that it would track aggregate patterns in the future, but in a way that is more consistent with methods used by other service providers.

The issue was made public on Tuesday when The Associated Press reported on Comcast's activities, which the company initially defended.

The policy change was applauded by Representative Edward J. Markey, Democrat of Massachusetts, who earlier in the day had written a letter to Comcast criticizing its behavior. In his letter, Mr. Markey expressed concern that Comcast's traffic tracking violated federal privacy provisions. But the congressman said in a statement that the change in policy offered reassurance to consumers.

Comcast, based in Philadelphia, first began tracking aggregate surfing patterns about six weeks ago, when it began rapid - and rocky - deployment of its cable modem service. Before the deployment, Comcast had offered its Internet service through a partnership with Excite@Home (news/quote), which filed for bankruptcy last year.

In its effort to deploy a network to replace Excite, Comcast upset many customers, particularly in New Jersey, who complained that their service was disrupted and that they could not get access to e-mail or the Web.

Before its bankruptcy, Excite@Home had been responsible for delivering Web pages to subscribers of the service, and, in turn, for tracking which sites were visited.

Privacy advocates and Internet industry experts said such a practice was common. But after Comcast sought to create its own version of the practice to replace Excite@Home's effort, some privacy advocates expressed concern. Specifically, critics said that Comcast left open the possibility that it could wed two databases, one with individual customer information and the other of aggregate surfing habits.

"The idea is that basically all my online activity is subject to logging," David Sobel, general counsel for the Electronic Privacy Information Center, said of the policy before the change. "This is the Internet-privacy horror story that everyone is concerned about."