Since the Sept. 11, 2001, attacks, the Justice Department and FBI have dramatically increased the use of two little-known powers that allow authorities to tap telephones, seize bank and telephone records and obtain other information in counterterrorism investigations with no immediate court oversight, according to officials and newly disclosed documents.

The FBI, for example, has issued scores of "national security letters" that require businesses to turn over electronic records about finances, telephone calls, e-mail and other personal information, according to officials and documents. The letters, a type of administrative subpoena, may be issued independently by FBI field offices and are not subject to judicial review unless a case comes to court, officials said.

Attorney General John D. Ashcroft has also personally signed more than 170 "emergency foreign intelligence warrants," three times the number authorized in the preceding 23 years, according to recent congressional testimony.

Federal law allows the attorney general to issue unilaterally these classified warrants for wiretaps and physical searches of suspected terrorists and other national security threats under certain circumstances. They can be enforced for 72 hours before they are subject to review and approval by the ultra-secret Foreign Intelligence Surveillance Court.

Government officials describe both measures as crucial tools in the war on terrorism that allow authorities to act rapidly in the pursuit of potential threats without the delays that can result from seeking a judge's signature. Authorities also stress that the tactics are perfectly legal.

But some civil liberties and privacy advocates say they are troubled by the increasing use of the tactics, primarily because there is little or no oversight by courts or other outside parties. In both cases, the target of the investigation never has to be informed that the government has obtained his personal records or put him under surveillance.

"When this kind of power is used in the regular criminal justice system, there are some built-in checks and balances," said David Sobel, general counsel of the Electronic Privacy Information Center (EPIC), which is suing the Justice Department for information about its secretive anti-terrorism strategies. "The intelligence context provides no such protection. That's the main problem with these kinds of secretive procedures."

The use of national security letters has been accelerated in part because Congress made it easier to use and apply them. The USA Patriot Act, a package of sweeping anti-terrorism legislation passed after the Sept. 11 attacks, loosened the standard for targeting individuals by national security letters and allowed FBI field offices, rather than a senior official at headquarters, to issue them, officials said.

The records that can be obtained through the letters include telephone logs, e-mail logs, certain financial and bank records and credit reports, a Justice official said.

The Patriot Act also significantly increased the amount of intelligence information that can be shared with criminal prosecutors and federal grand juries, giving authorities new powers in the war on terrorism. National security letters can be used as part of criminal investigations and preliminary inquiries involving terrorism and espionage, according to officials and internal FBI guidelines on the letters.

According to documents given to EPIC and the American Civil Liberties Union as part of their lawsuit, the FBI has issued enough national security letters since October 2001 to fill more than five pages of logs. There is no way to determine exactly how many times the documents have been employed because the logs were almost entirely blacked out, according to a copy provided to The Washington Post by the ACLU.

The Justice Department and FBI refuse to provide summary data about how often the letters are used. Several lawmakers have proposed legislation that would require the department to provide that kind of data.

"In our view, the public is entitled to these statistics," said Jameel Jaffer, staff attorney for the ACLU's national legal department. "We have no idea how those are being used."

FBI spokesman John Iannarelli said "it's safe to say that anybody who is going to conduct a terrorism investigation is probably going to use them at some point. . . . It's a way to expedite information, and there's nothing that needs expediting more than a terrorism investigation."

But a November 2001 memorandum prepared by FBI attorneys warned that the letters "must be used judiciously" to avoid angering Congress, which will reconsider Patriot provisions in 2005. "The greater availability of NSLs does not mean they should be used in every case," the memo says.

Beryl A. Howell, former general counsel to Sen. Patrick Leahy (D-Vt.) and a specialist in surveillance law, described national security letters as "an unchecked, secret power that makes it invisible to public scrutiny and difficult even for congressional oversight." Howell now is a managing director and general counsel at Stroz Friedberg LLC, a computer forensic firm in the District.

Under the Foreign Intelligence Surveillance Act (FISA), the government has the power to obtain secret warrants for telephone wiretaps, electronic monitoring and physical searches in counterterrorism and espionage cases. The Justice Department has expanded its use of such warrants since a favorable FISA court ruling last year, which determined that the Patriot Act gave federal officials broad new authority to obtain them.

The warrants, cloaked in secrecy and largely ignored by the public for years, have become a central issue in the ongoing debate over missteps before the Sept. 11 attacks. The FBI has come under sharp criticism from lawmakers who say FBI officials misread the FISA statute in the case of Zacarias Moussaoui, the alleged terror conspirator who was in custody before the attacks. No warrant was sought in the Moussaoui case, and his computer and other belongings were not searched until after the attacks.

Even less well known are provisions that allow the attorney general to authorize these secret warrants on his own in emergency situations. The department then has 72 hours from the time a search or wiretap is launched to obtain approval from the FISA court, whose proceedings and findings are closed to the public.

Officials said that Ashcroft can use his emergency power when he believes there is no time to wait for the FISA court to approve a warrant. There are no additional restrictions on emergency warrants, other than the rules that apply to all FISA applications, officials said.

Ashcroft told lawmakers earlier this month that Justice made more than 1,000 applications for warrants to the secret court in 2002, including more than 170 in the emergency category. In the previous 23 years, only 47 emergency FISA warrants were issued.

FBI Director Robert S. Mueller III, in similar testimony to the Senate Judiciary Committee, said, "We can often establish electronic surveillance within hours of establishing probable cause that an individual is an appropriate FISA subject."

"We have made full and very productive use of the emergency FISA process," Mueller said.

Sobel and other civil liberties advocates say they are troubled by the aggressive use of emergency FISAs because it leaves the initial decision up to the attorney general and allows clandestine searches and surveillance for up to three days before any court review.

Staff researcher Madonna Lebling contributed to this report.

Attorney General John D. Ashcroft told lawmakers this month that he has filed over 1,000 applications with the Foreign Intelligence Surveillance Court.