The presiding judge of a secret court that oversees government surveillance in espionage and terrorism cases is arranging a classified briefing for her fellow judges to address their concerns about the legality of President Bush's domestic spying program, according to several intelligence and government sources.

Several members of the Foreign Intelligence Surveillance Court said in interviews that they want to know why the administration believed secretly listening in on telephone calls and reading e-mails of U.S. citizens without court authorization was legal. Some of the judges said they are particularly concerned that information gleaned from the president's eavesdropping program may have been improperly used to gain authorized wiretaps from their court.

"The questions are obvious," said U.S. District Judge Dee Benson of Utah. "What have you been doing, and how might it affect the reliability and credibility of the information we're getting in our court?"

Such comments underscored the continuing questions among judges about the program, which most of them learned about when it was disclosed last week by the New York Times. On Monday, one of 10 FISA judges, federal Judge James Robertson, submitted his resignation -- in protest of the president's action, according to two sources familiar with his decision. He will maintain his position on the U.S. District Court here.

Other judges contacted yesterday said they do not plan to resign but are seeking more information about the president's initiative. Presiding Judge Colleen Kollar-Kotelly, who also sits on the U.S. District Court for the District of Columbia, told fellow FISA court members by e-mail Monday that she is arranging for them to convene in Washington, preferably early next month, for a secret briefing on the program, several judges confirmed yesterday.

Two intelligence sources familiar with the plan said Kollar-Kotelly expects top-ranking officials from the National Security Agency and the Justice Department to outline the classified program to the members.

The judges could, depending on their level of satisfaction with the answers, demand that the Justice Department produce proof that previous wiretaps were not tainted, according to government officials knowledgeable about the FISA court. Warrants obtained through secret surveillance could be thrown into question. One judge, speaking on the condition of anonymity, also said members could suggest disbanding the court in light of the president's suggestion that he has the power to bypass the court.

The highly classified FISA court was set up in the 1970s to authorize secret surveillance of espionage and terrorism suspects within the United States. Under the law setting up the court, the Justice Department must show probable cause that its targets are foreign governments or their agents. The FISA law does include emergency provisions that allow warrantless eavesdropping for up to 72 hours if the attorney general certifies there is no other way to get the information.

Still, Bush and his advisers have said they need to operate outside the FISA system in order to move quickly against suspected terrorists. In explaining the program, Bush has made the distinction between detecting threats and plots and monitoring likely, known targets, as FISA would allow.

Bush administration officials believe it is not possible, in a large-scale eavesdropping effort, to provide the kind of evidence the court requires to approve a warrant. Sources knowledgeable about the program said there is no way to secure a FISA warrant when the goal is to listen in on a vast array of communications in the hopes of finding something that sounds suspicious. Attorney General Alberto R. Gonzales said the White House had tried but failed to find a way.

One government official, who spoke on the condition of anonymity, said the administration complained bitterly that the FISA process demanded too much: to name a target and give a reason to spy on it.

"For FISA, they had to put down a written justification for the wiretap," said the official. "They couldn't dream one up."

The NSA program, and the technology on which it is based, makes it impossible to meet that criterion because the program is designed to intercept selected conversations in real time from among an enormous number relayed at any moment through satellites.

"There is a difference between detecting, so we can prevent, and monitoring. And it's important to note the distinction between the two," Bush said Monday. But he added: "If there is a need based upon evidence, we will take that evidence to a court in order to be able to monitor calls within the United States."

The American Civil Liberties Union formally requested yesterday that Gonzales appoint an outside special counsel to investigate and prosecute any criminal acts and violations of laws as a result of the spying effort.

Also yesterday, John D. Negroponte, Bush's director of national intelligence, sent an e-mail to the entire intelligence community defending the program. The politically tinged memo referred to the disclosure as "egregious" and called the program a vital, constitutionally valid tool in the war against al Qaeda.

Benson said it is too soon for him to judge whether the surveillance program was legal until he hears directly from the government.

"I need to know more about it to decide whether it was so distasteful," Benson said. "But I wonder: If you've got us here, why didn't you go through us? They've said it's faster [to bypass FISA], but they have emergency authority under FISA, so I don't know."

As it launched the dramatic change in domestic surveillance policy, the administration chose to secretly brief only the presiding FISA court judges about it. Officials first advised U.S. District Judge Royce C. Lamberth, the head of FISA in the fall of 2001, and then Kollar-Kotelly, who replaced him in that position in May 2002. U.S. District Judge George Kazen of the Southern District of Texas said in an interview yesterday that his information about the program has been largely limited to press accounts over the past several days.

"Why didn't it go through FISA," Kazen asked. "I think those are valid questions. The president at first said he didn't want to talk about it. Now he says, 'You're darn right I did it, and it's completely legal.' I gather he's got lawyers telling him this is legal. I want to hear those arguments." Judge Michael J. Davis of Minnesota said he, too, wants to be sure the secret program did not produce unreliable or legally suspect information that was then used to obtain FISA warrants.

"I share the other judges' concerns," he said.

But Judge Malcolm Howard of eastern North Carolina said he tends to think the terrorist threat to the United States is so grave that the president should use every tool available and every ounce of executive power to combat it.

"I am not overly concerned" about the surveillance program, he said, but "I would welcome hearing more specifics."

Researcher Julie Tate contributed to this report.

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