Since the 2001 terror attacks, Attorney General John Ashcroft has approved more than 170 emergency domestic spying warrants, triple the number used in the previous 23 years.

The emergency warrants, authorized under the Foreign Intelligence Surveillance Act, permit authorities to tap telephones and fax numbers and conduct physical searches for up to 72 hours before they are subject to review by the special, secret Foreign Intelligence Surveillance Court.

In testimony to Congress earlier this month, Ashcroft said there were more than 1,000 applications for FISA warrants in 2002, including the emergency warrants. The attorney general said the accelerated use of FISA warrants, authorized by the U.S. Patriot Act that Congress passed just after the 2001 attacks, is one reason there has been no further terrorist attacks in this country.

"We are gathering and cultivating detailed intelligence on terrorism in the United States," Ashcroft told the Senate Judiciary Committee on March 4.

Yet the secrecy surrounding the warrants and their targets, who may never know they were under surveillance, gives civil liberties groups and some lawmakers pause. Sens. Patrick Leahy, D-Vt., and Charles Grassley, R-Iowa, are sponsoring legislation that would require the Justice Department to publicly account for the use of FISA warrants.

Several privacy activist groups are suing the Justice Department in federal court to get the same information.

"Disclosure of basic information about FISA surveillance is not going to hamper our anti-terrorism efforts, nor will it hamstring Justice's law enforcement efforts," said Timothy Edgar, legislative counsel for the American Civil Liberties Union. "What it will do ... is go a long way toward assuaging growing public mistrust of the government."

The FBI also has stepped up its use of what are called "national security letters," which require businesses to turn over financial records, e-mail and other information. Officials declined Monday to provide exact numbers of these letters, which are subject to court review only if the case reaches a court