Several years ago, officials at the National Security Agency, the secretive "Puzzle Palace" on the Baltimore-Washington Expressway, sought to reassure taxpayers that the agency had long since repudiated its Vietnam-era spying on U.S. citizens.
They insisted that the movie Enemy of the State, which portrayed NSA as using its formidable technology to track and eavesdrop on Americans, was the stuff of Hollywood fantasy.
Now NSA stands accused of abetting the White House in what civil liberties activists and others describe as a frontal assault on the constitutional right to privacy.
The program reportedly traced thousands of calls from phones linked to terror suspects to and from locations in the United States, and then listened in on many of those conversations - all without seeking warrants from a special foreign intelligence court. E-mails were also tracked and read, according to news reports.
"I've stuck up for NSA innumerable times, saying I didn't believe they were engaged in illegal activity," said James Bamford, author of two acclaimed books on the NSA, The Puzzle Palace and Body of Secrets. But now, he said, there is no question that after the Sept. 11 attacks the agency broke the law.
Revelations about the warrantless surveillance effort, he said, have thrown the nation's largest and most secretive intelligence-gathering organization into turmoil.
"Most of the people I've dealt with there had no idea this was going on, and they were very shocked and disappointed that suddenly they're back to where they were 30 years ago, dealing with questions of domestic spying," he said.
Don Weber, an NSA spokesman, said in a telephone interview last week that the agency can't comment on operational issues in the interests of national security.
The surveillance effort will be subject to congressional hearings, expected to begin in the next several weeks.
Sen. Arlen Specter of Pennsylvania, the Republican chairman of the Senate Judiciary Committee, told The New York Times that he planned to hold hearings on the surveillance program after confirmation hearings for Judge Samuel A. Alito Jr. to the Supreme Court. Those hearings are expected to stretch into late January or early February.
According to reports in The New York Times and elsewhere, NSA launched the program almost immediately after the September 2001 attacks, before President Bush issued a secret order authorizing it.
Bamford and others contend that, with or without presidential approval, the program was conducted in violation of the 1978 Foreign Intelligence Surveillance Act.
That law prohibits NSA from intercepting calls or other electronic communications to or from a U.S. citizen or resident alien without a warrant from the Foreign Intelligence Surveillance Court.
Bamford, who holds a law degree, said the statute was written "to prevent exactly what just happened." Some critics are calling the president's authorization of the program an impeachable offense.
"The eventual outcome will be a special prosecutor," predicted Bamford. "Of course it's an impeachable offense."
The Bush administration, meanwhile, has stood stalwartly by the program, saying that president had the authority to authorize it based on his powers as commander in chief of the armed forces.
Not only has the White House refused to cancel the program, the government has launched an investigation against the whistle-blowers who leaked the story to the Times.
To its defenders, the NSA program was not just legal. It was a vital and necessary part of the efforts to prevent another Sept. 11-style attack.
"It was an integral and important part of the nation's counter-terrorism toolkit," said John E. McLaughlin, who served as deputy director of the CIA from 2000 to 2004 and was briefed on the program.
"People should understand this wasn't a huge drift net hanging over Detroit or Florida or California, scooping up communications," said McLaughlin, now retired from the CIA and a visiting scholar at the Johns Hopkins University School of Advanced International Studies.
"There had to be a foreign connection, and there had to be a reasonable belief that one of the parties involved had to be in contact with a terrorist or was a terrorist. So the whole idea that this was the NSA pawing through great volumes of information among Americans was not right."
Vice President Dick Cheney, in a speech at the Heritage Foundation last week, said that the program was "fully consistent with the constitutional responsibilities and legal authority of the president and with the civil liberties of the American people."
If it had been in place before Sept. 11, he said, two of the hijackers who flew a jet into the Pentagon might have been captured.
But to critics, the alleged abuses are so serious that they eclipse even concerns of future terror attacks.
"What makes this such an urgent matter is that it calls into question the rule of law," said Steven Aftergood, the director of the Project on Government Secrecy at the Federation of American Scientists.
"If the president is at liberty to circumvent the law, then where does his authority stop?" he said. "We have already seen American citizens detained as enemy combatants. We have seen international conventions against torture reinterpreted to permit extreme forms of interrogation. We are in the process of undermining the rules which define us as a democracy. And that makes this scary."
The upcoming hearings, planned for the intelligence and judiciary committees in the Senate and House, will lead lawmakers into the NSA's arcane world of electronic eavesdropping, where information is measured in billions of bits and data is mined like veins of precious metal.
Congress will focus on a few key questions: What kinds of surveillance did the agency conduct? Were legislators fully informed about the program? Were abuses committed? And, of course: Was the program legal?
The search for answers might be difficult.
For one thing, the strategies and hardware NSA uses are among the American government's most closely held secrets, and it is not clear to what extent the administration will be willing to discuss them.
"If someone insists on going into the details of how this was done and precisely what was done, it will become harder to chase and capture terrorists and deter them," McLaughlin said.
The mere disclosure of the program's existence, he said, has harmed the war against terror. "I'm a little surprised that there has been so little concern about the impact on our counter-terrorism capabilities," he said. "It will be less effective, because the bad guys are on notice."
Another key issue is whether Congress was fully informed about the surveillance efforts. The administration insists it was. Some legislators aren't so sure.
"Leaders of Congress have been briefed more than a dozen times" on the NSA program, Cheney said last week. "I have personally presided over most of those briefings."
Yet critics say the highly technical briefings may have left some Congressional leaders more confused than enlightened, perhaps as part of a deliberate White House strategy.
"As you know, I am neither a technician nor an attorney," Sen. John D. Rockefeller IV, a West Virginia Democrat, wrote Cheney hours after a July 2003 briefing on the NSA surveillance program. "Given the security restrictions associated with this information, and my inability to consult staff or counsel on my own, I feel unable to fully evaluate, much less endorse these activities."
One former senior administration official familiar with NSA issues rejected this criticism. "I was in at least one of those briefings, and what I recall is that the program was very thoroughly explained to them," said the official, who commented on condition that he not be identified.
Ruth Wedgewood of Johns Hopkins' School of Advanced International Studies, who sits on Secretary of Defense Donald H. Rumsfeld's Defense Policy Advisory Board, said the White House probably felt it had no choice but to limit access to the information.
"It really is a problem of, how do you inform people and not have stuff leak immediately?" she said.
Civil liberties advocates ask why, if expanded NSA surveillance powers were needed, the White House didn't simply seek them.
The Foreign Intelligence Service Act has been expanded twice since Sept. 11, once in the original Patriot Act and a second time in December 2004.
But McLaughlin said that any effort to change the law "would probably have involved a debate that would have risked exposing the methods and techniques of the program, and would therefore have rendered it" less effective.
Others asked how the NSA could possibly have asked for court permission to track thousands of calls in real time, as it may have done.
Wedgewood pointed out that the 1978 surveillance act, known as FISA, was written in an era before e-mail, the Internet and the widespread use of desktop computers.
"The new technology was something the FISA wasn't necessarily designed to encompass," she said.
Congress may look at possible connections between the NSA's surveillance effort and the Total Information Awareness program, created by the Defense Advanced Research Projects Agency, or DARPA, in January 2002.
DARPA set out to perfect the tools of "data mining" - the trolling of public computer databases in a hunt for suspicious patterns that could point to terrorist activity. At the time, the agency insisted it was merely a research project.
The DARPA program was led by Adm. John M. Poindexter, a key figure in the Iran-Contra scandal of the 1980s, in which the proceeds from the secret sale of arms to Iran were diverted to right-wing Nicaraguan rebels.
Shortly after The New York Times disclosed existence of the program, DARPA abandoned it. Poindexter later left the government.
No matter what the hearings find, they will almost certainly draw the veil a little further from the secretive agency.
"The facts of the operation are still obscure, and every day we seem to learn something new," said Aftergood of the Federation of American Scientists.
Now, he said, it is up to the government to justify what it has done. "The burden really falls on the NSA and the administration to re-establish its credibility," Aftergood said. "Because this whole operation is at odds with what they have been telling us for years."