It has been nearly two years since the Patriot Act's swift adoption in the wake of the September 11, 2001, terrorist attacks on the United States. But whether the law is the boon to law enforcement claimed by its supporters or the menace to civil liberties feared by its foes remains unclear.

Among its many provisions, the wide-ranging antiterrorism act defines new crimes such as bulk cash smuggling and attacks against mass transit systems, calls for greater information sharing among intelligence agencies, expands the scope of laws dealing with money laundering, and toughens immigration rules for aliens suspected of engaging in terrorist activities.

A major focus of the Patriot Act is on electronic surveillance. Among the act's innovations are provisions that allow federal law enforcement and intelligence agencies to use certain techniques that were previously restricted to telephone communications to collect information about Internet users. Notably, the agencies are authorized to trace users' visits to Web sites and to identify their e-mail correspondents, without reading the actual messages.

In addition, the act requires a wide array of businesses and agencies to collect detailed information about groups and individuals and to relay the information to federal agencies, including data about users of the Internet.

Federal authorities say that the Patriot Act simply gives law enforcement 21st-century tools for combating terrorism, and that it contains ample safeguards to protect civil rights. They say that it has enabled them to file criminal charges against 255 suspects and to dismantle four terrorist cells operating in the United States.

"The Patriot Act gives investigators the ability to fight terror, using many of the court-approved tools that have been used successfully for many years in drug, fraud, and organized crime cases," U.S. Attorney General John Ashcroft said in a recent speech in Boise, Idaho.

Critics such as the American Civil Liberties Union (ACLU) and the Electronic Privacy Information Center (EPIC) charge that the law is too invasive and violates Constitutional guarantees against unreasonable search and seizure. So far, however, little is known about how the government is invoking the act's provisions, and exactly what it does with the data gathered under it.

Last year, the ACLU, EPIC, and several other free-speech organizations filed a lawsuit under the Freedom of Information Act against the Department of Justice, trying to obtain documents detailing how the law is being used.

The suit was dismissed this spring, but not before the ACLU obtained a six-page list of Justice Department electronic surveillance orders approved under the act between October 2001 and January 2003. Virtually all of the information was blacked out for security reasons. Justice Department officials even deleted the total number of orders obtained.

A Congressional request for a similar status report yielded limited public disclosure.

Opening a second front on the topic, this summer the ACLU filed suit against U.S. Attorney General John Ashcroft and U.S. Federal Bureau of Investigation (FBI) Director Robert Mueller. The group seeks a court ruling that a specific provision of the Act, Section 215, is unconstitutional.

One of the most controversial provisions of the Act, Section 215 prohibits any individual or organization from revealing that it has given records to the federal government pursuant to a Patriot Act investigation.