Bomb plots targeting the New York Stock Exchange and the city's subway were among more than 50 terrorist acts worldwide thwarted by top-secret surveillance programs since the 2001 al Qaeda attacks on the United States, security officials said Tuesday.
The startling details disclosed at a House intelligence committee hearing reflected a unified effort by the Obama administration and legislators to defend the telephone and e-mail surveillance made public this month by classified leaks to newspapers.
Testimony by Gen. Keith Alexander, the National Security Agency director, as well as officials from the FBI, Department of Justice and the Director of National Intelligence office called the programs created under the Patriot Act in the aftermath of the 9/11 attacks a vital tool against terrorist plots.
Joined by panel Chairman Rep. Mike Rogers and other legislators, they condemned the document leaks by former government contractor Edward Snowden as harmful to the United States and its allies.
The leaks also led to what officials called widespread public misinformation about the surveillance programs that necessitated the relatively rare open hearing by the intelligence panel, where they detailed previously classified information in order to set the record straight.
It was the most comprehensive and specific defense of the surveillance methods that have come under ferocious criticism from civil liberties groups, some members of Congress and others concerned about the reach of government into the private lives of citizens.
National security and law enforcement officials repeated that the programs are tightly run with significant regulation and oversight by federal judges and Congress.
Addressing the most basic questions that have emerged, Rogers asked Alexander if intelligence workers have the ability to simply "flip a switch" in order to listen to phone calls or read the emails of Americans.
When Alexander replied "no," Rogers asked again to reinforce the message for anyone listening.
"So the technology does not exist for any individual or group of individuals at the NSA to flip a switch to listen to Americans' phone calls or read their e-mails?" he repeated.
"That is correct," Alexander answered.
He and others also asserted that the leaks were egregious and carry huge consequences for national security.
"I think it was irreversible and significant damage to this nation," Alexander said when questioned by Rep. Michele Bachmann.
"Has this helped America's enemies?" the conservative Minnesota Republican asked.
"I believe it has and I believe it will hurt us and our allies," Alexander said.
President Barack Obama has defended the programs as necessary in an era of terror.
In an interview with PBS' Charlie Rose broadcast on Monday night, Obama said the situation requires a national debate on the balance between security and privacy.
Alexander told a Senate committee last week that the surveillance programs helped stop dozens of terror plots, but he was unable then to provide classified details.
Under pressure from Rogers and other legislators, Alexander joined law enforcement officials Tuesday in making public some declassified details of the Patriot Act provisions.
In recent years, Alexander said, information "gathered from these programs provided government with critical leads to prevent over 50 potential terrorist events in more than 20 countries around the world."
Details of most of the thwarted terrorism acts remain secret, but national security officials said they were working on declassifying more information and could have a report to Congress as early as this week.
Sean Joyce, the deputy FBI director, detailed how email surveillance of foreigners under one program helped authorities discover the two New York City plots.
In the fall of 2009, Joyce said, the NSA intercepted an e-mail from a suspected terrorist in Pakistan. That person was talking with someone in the United States "about perfecting a recipe for explosives," he said.
Authorities identified Afghan-born Najibullah Zazi of Denver. The FBI followed him to New York and eventually broke up planning to attack the city's subway system. Zazi pleaded guilty and is currently in prison.
In the other New York case, the NSA was monitoring a "known extremist" in Yemen who was in contact with a person in the United States, Joyce said. The FBI detected "nascent plotting" to bomb the stock exchange, long considered a target of terrorists, and the plotters were later convicted, according to Joyce.