Most members of the Senate Intelligence Committee have agreed to provide the FBI with details of their contacts with reporters as part of an investigation into leaks of classified information from a congressional inquiry into the Sept. 11 attacks.

Journalists and First Amendment advocates said they were troubled by the prospect of the FBI collecting information on communications between reporters and lawmakers. It threatens the confidentiality essential to newsgathering, they said.

"Obviously it's an issue that ultimately has a chilling effect on the flow of information from official sources to the public," said Douglas Clifton, editor of The Plain Dealer in Cleveland and chairman of the American Society of Newspaper Editors' Freedom of Information Committee.

The FBI investigation comes as the Justice Department seeks to block public disclosure by Congress of the results of its investigation of Zacarias Moussaoui, the only person charged in the United States in connection with the Sept. 11 attacks.

In court papers unsealed Thursday in Alexandria, Va., prosecutors said they don't object to plans by the House and Senate intelligence committees to disclose what the government knows about the planning and execution of the attacks or what was known about two hijackers who met with Al Qaeda operatives in Malaysia in January 2000, shortly before they came to the United States.

But the government said planned September hearings into the FBI's investigation of Moussaoui while he was in custody before the attacks could jeopardize his trial, now set for January. Lawyers for the committees said the hearings would not delve into Moussaoui's guilt or innocence.

U.S. District Judge Leonie Brinkema refused for the time being to interfere with the hearings. But she asked prosecutors to propose new rules for handling sensitive material from the Moussaoui case that might be made public during congressional hearings.

The FBI is trying to determine who leaked details of conversations intercepted by the National Security Agency that were discussed June 18 at the House and Senate intelligence committees' closed-door inquiry. Details of the Arabic intercepts were broadcast the next day. The committees had requested the investigation.

The Justice Department sent a letter to the Senate counsel's office Aug. 7 requesting that members of the Senate committee and their press staff submit telephone logs, memos, visitor sign-in sheets and other material showing communications with the news media between noon June 18 and 3:15 p.m. June 19, when details of the intercepts were broadcast on television.

The letter also called for calendars, appointment books and e-mails for the senators and their press staff during that period. No similar request was made of House Intelligence Committee members.

Contacted Thursday by The Associated Press, the offices of 13 of the 17 committee members said they are complying with the request. No office said it wasn't. In the other four offices, information wasn't available because the senator was traveling.

The committee's chairman, Sen. Bob Graham, D-Fla., has instructed his staff to compile the material requested, said his spokesman, Paul Anderson.

Anderson said Graham supports the FBI investigation because the leak of classified information violated the law. The FBI also could examine whether the leaks may have come from outside Congress, he said. An internal investigation might not be able to do so.

Graham "has said that he has nothing to hide and no reason to fear sharing his schedules and appointments," he said.

But Paul McMasters of Freedom Forum's First Amendment Center said the FBI investigation could go beyond the leak and uncover unrelated communications between lawmakers and journalists.

"That's where this problem comes in," he said. Freedom Forum is an Arlington, Va.-based foundation dedicated to press freedom.

Caesar Andrews, president of Associated Press Managing Editors, said the request for information about press contacts "creates a mood of fear and dread among those people who should be helping to put the U.S. efforts in context."

"I think it's more the climate that's created when there's a sense of overly aggressive efforts to clamp down on information," said Andrews, editor of Gannett News Service.

Some lawmakers, including the panel's top Republican, Sen. Richard Shelby of Alabama, have said the FBI investigation of the committees breaches the separation of powers between the executive and legislative branches -- particularly while the committee is examining intelligence shortcomings at the FBI and other agencies.

Sen. Richard Durbin, R-Ill., told the Chicago Sun-Times this week that in requesting personal schedules, the FBI was "trying to put a damper on our activities and I think they will be successful." He was unavailable for comment Thursday.

Members of the inquiry have been interviewed by the FBI, but some objected when the FBI asked if they would consider taking lie detectors.

But lawmakers haven't raised the issue of whether submitting materials to the FBI could have a chilling effect on the press.

Mike Dawson, a spokesman for Sen. Mike DeWine, R-Ohio, said, "It's always a concern, but he believes that the leaks are serious and he's going to cooperate."

The leaked information was conversations intercepted by the NSA on Sept. 10, but not translated until Sept. 12. An intelligence source told The Associated Press they contained the phrases, "Tomorrow is zero hour" and "The match is about to begin."

The leaks angered the White House and led Vice President Dick Cheney to complain to committee leaders.