The U.S. Department of Justice is quietly shopping around the explosive idea of requiring Internet service providers to retain records of their customers' online activities.

Data retention rules could permit police to obtain records of e-mail chatter, Web browsing or chat-room activity months after Internet providers ordinarily would have deleted the logs--that is, if logs were ever kept in the first place. No U.S. law currently mandates that such logs be kept.

In theory, at least, data retention could permit successful criminal and terrorism prosecutions that otherwise would have failed because of insufficient evidence. But privacy worries and questions about the practicality of assembling massive databases of customer behavior have caused a similar proposal to stall in Europe and could engender stiff opposition domestically.

In Europe, the Council of Justice and Home Affairs ministers say logs must be kept for between one and three years. One U.S. industry representative, who spoke on condition of anonymity, said the Justice Department is interested in at least a two-month requirement.

Justice Department officials endorsed the concept at a private meeting with Internet service providers and the National Center for Missing and Exploited Children, according to interviews with multiple people who were present. The meeting took place on April 27 at the Holiday Inn Select in Alexandria, Va.