The subcommittee wants to discuss concerns that applying the new technology violates statutes protecting citizens from unreasonable searches and seizures.
Criticism of Carnivore has made strange bedfellows since word of it became public this month, with a core of Republican leaders and the American Civil Liberties Union (ACLU) expressing concern over the technology's potential for abuse by the law enforcement community.
But the system is not new and is not a secret, officials said. The FBI has been using the system for about three years and has briefed government and industry leaders about it, bureau officials said.
In some cases, the Carnivore system, developed by the bureau, has not even been fielded for e-mail taps. Instead, Internet service providers, some of which have their own sophisticated monitors, have provided the bureau with information under court order, FBI officials said.
The officials, who provided the Carnivore demonstration on condition of anonymity, said the standards guiding the tapping of e-mail are the same as those for traditional telephone wiretaps. However, Carnivore can be so narrowly focused that extraneous information - such as personal conversations by people other than the subject of an investigation - is not collected.
At the briefing, a laptop computer stood in for a small, stackable computer that would normally be deployed for an Internet tap. Its color screen showed a menu that agents would use to target an e-mail account.
Agents target e-mail in much the same way a computer user would define a search of a database or document - by describing what to look for and what not to look for. As the search criteria is keyed in, the data takes the shape of a pyramid on its side as it narrows in on e-mail specifically targeted by officials and spelled out in a court order authorizing the tap.
As an ISP transmits e-mail, Carnivore copies those messages with the targeted individual's ISP number - the equivialent of a phone number - and sends it through a filter that retains on tape or disk only those e-mail messages meeting the criteria programmed by agents into Carnivore.
In most cases, FBI officials said, the information plucked from e-mail messages consists of the "To" and "From" identification and does not even include the subject line. But the FBI can and has intercepted e-mail messages in their entirety, officials acknowledged.