"All too often, we find that before we can catch these offenders, Internet service providers have unwittingly deleted the very records that would help us identify these offenders and protect future victims," Mueller said. "We must find a balance between the legitimate need for privacy and law enforcement's clear need for access."

The speech to the law enforcement group, which approved a resolution on the topic earlier in the day, echoes other calls from Bush administration officials to force private firms to record information about customers. Attorney General Alberto Gonzales, for instance, told Congress last month that "this is a national problem that requires federal legislation."

Justice Department officials admit privately that data retention legislation is controversial enough that there wasn't time to ease it through the U.S. Congress before politicians left to campaign for re-election. Instead, the idea is expected to surface in early 2007, and one Democratic politician has already promised legislation.

Law enforcement groups claim that by the time they contact Internet service providers, customers' records may have been deleted in the routine course of business. Industry representatives, however, say that if police respond to tips promptly instead of dawdling, it would be difficult to imagine any investigation that would be imperiled.

It's not clear exactly what a data retention law would require. One proposal would go beyond Internet providers and require registrars, the companies that sell domain names, to maintain records too. And during private meetings with industry officials, FBI and Justice Department representatives have cited the desirability of also forcing search engines to keep logs--a proposal that could gain additional law enforcement support after AOL showed how useful such records could be in investigations.

A representative of the International Association of Chiefs of Police said he was not able to provide a copy of the resolution.

Preservation vs. retention
At the moment, Internet service providers typically discard any log file that's no longer required for business reasons such as network monitoring, fraud prevention or billing disputes. Companies do, however, alter that general rule when contacted by police performing an investigation--a practice called data preservation.

A 1996 federal law called the Electronic Communication Transactional Records Act regulates data preservation. It requires Internet providers to retain any "record" in their possession for 90 days "upon the request of a governmental entity."

Because Internet addresses remain a relatively scarce commodity, ISPs tend to allocate them to customers from a pool based on whether a computer is in use at the time. (Two standard techniques used are the Dynamic Host Configuration Protocol and Point-to-Point Protocol over Ethernet.)

In addition, Internet providers are required by another federal law to report child pornography sightings to the National Center for Missing and Exploited Children, which is in turn charged with forwarding that report to the appropriate police agency.

When adopting its data retention rules, the European Parliament approved U.K.-backed requirements saying that communications providers in its 25 member countries--several of which had enacted their own data retention laws already--must retain customer data for a minimum of six months and a maximum of two years.

The Europe-wide requirement applies to a wide variety of "traffic" and "location" data, including: the identities of the customers' correspondents; the date, time and duration of phone calls, VoIP (voice over Internet Protocol) calls or e-mail messages; and the location of the device used for the communications. But the "content" of the communications is not supposed to be retained. The rules are expected to take effect in 2008.

CNET News.com's Anne Broache contributed to this report.