The Senate Judiciary Committee on Monday continued to press the FBI on Carnivore, the surveillance tool said capable of capturing and storing all electronic traffic moving through an Internet gateway.

Committee Chairman Orrin Hatch, a Utah Republican, and ranking Democrat Patrick Leahy of Vermont asked FBI Director Louis Freeh to spell out Carnivore's reach and address concerns that it might trample on constitutional rights.

The system is installed at an Internet service provider to keep court-ordered tabs on a criminal suspect's email and instant messages.

The FBI previously has told the panel -- concerned about a breach of Fourth Amendment protection against unreasonable search and seizure -- that Carnivore captures only a narrow field of information for which interception is authorized.

Specifically, this information is either source and destination data in the case of a court-ordered "trap and trace" operation or full messages in a wiretap order, FBI Assistant Director Donald Kerr told the panel September 6.

In a November 21 letter to Freeh, Hatch and Leahy cited records of a test showing Carnivore "could reliably capture and archive all unfiltered traffic" transmitted through an ISP and store the communications on a hard drive or removable disks.

The June 5 document at issue was produced by the FBI in response to a lawsuit under the Freedom of Information Act by the Electronic Privacy Information Center, a private Washington-based civil liberties organization.

"Please explain why Carnivore was tested to determine if it was capable of intercepting and archiving unfiltered traffic through an ISP, whether Carnivore in fact has that capability, and under what circumstances it could ever be legitimately used to draw on that capability," they asked Freeh.

Hatch and Leahy also asked for "complete and non-redacted copies" of documents handed over so far in response to the FOIA lawsuit together with "any other documents related to Carnivore's capability to intercept and archive unfiltered traffic."

"Skepticism about Carnivore is based precisely on concerns about this program's capability and whether this capability would be exploited to do more than just intercept narrowly targeted pieces of information," the senators told Freeh.

The FBI had no immediate comment on the letter, sent on the same day that the Justice Department released an outside review panel's draft report on Carnivore.

When correctly used, Carnivore "provides investigators with no more information than is permitted by a given court order," the IIT Research Institute, an arm of the Illinois Institute of Technology, said in its draft.

The institute called Carnivore potentially "more effective in protecting privacy and enabling lawful surveillance" than alternatives.

Attorney General Janet Reno ordered an independent review of Carnivore's inner workings after a stir in Congress. The Justice Department had no immediate comment on Hatch and Leahy's letter.

Assistant Attorney General Stephen Colgate, head of the review panel that will make recommendations to Reno on Carnivore, told Reuters last week that a new version of Carnivore "probably will begin being used shortly after the new year."

He said his panel would make recommendations to Reno on "improvements that need to be made in the system" after taking account of the outside review panel's suggestions.