National Security Agency Director Gen. Keith Alexander told members of the House Select Intelligence Committee these programs helped prevent a terrorist attack similar to 9/11. (The Washington Post)

The U.S. government’s sweeping surveillance programs have disrupted more than 50 terrorist plots in the United States and abroad, including a plan to bomb the New York Stock Exchange, senior government officials testified Tuesday.

The officials, appearing before a largely friendly House committee, defended the collection of telephone and Internet data by the National Security Agency as central to protecting the United States and its allies against terrorist attacks. And they said that recent disclosures about the surveillance operations have caused serious damage.

“We are now faced with a situation that, because this information has been made public, we run the risk of losing these collection capabilities,” said Robert S. Litt, general counsel of the Office of the Director of National Intelligence. “We’re not going to know for many months whether these leaks in fact have caused us to lose these capabilities, but if they do have that effect, there is no doubt that they will cause our national security to be affected.”

The hearing before the House Intelligence Committee was the third congressional session examining the leaks of classified material about two top-secret surveillance programs by Edward Snowden, 29, a former NSA contractor and onetime CIA employee.

Articles based on the material in The Washington Post and Britain’s Guardian newspaper have raised concerns about intrusions on civil liberties and forced the Obama administration to mount an aggressive defense of the effectiveness and privacy protections of the operations.

NSA Director Gen. Keith Alexander told members of Congress these programs are a “tool to...stop future attacks.” (The Washington Post)

Gen. Keith B. Alexander, the head of the NSA, told the committee that the programs had helped prevent “potential terrorist events over 50 times since 9/11.” He said at least 10 of the disrupted plots involved terrorism suspects or targets in the United States.

Alexander said officials do not plan to release additional information publicly, to avoid revealing sources and methods of operation, but he said the House and Senate intelligence committees will receive classified details of the thwarted plots.

Newly revealed plots

In testimony last week, Alexander said the surveillance programs had helped prevent an attack on the subway system in New York City and the bombing of a Danish newspaper. Sean Joyce, deputy director of the FBI, described two additional plots Tuesday that he said were stopped through the surveillance — a plan by a Kansas City, Mo., man to bomb the New York Stock Exchange and efforts by a San Diego man to send money to terrorists in Somalia.

The officials said repeatedly that the operations were authorized by Congress and subject to oversight through internal mechanisms and the Foreign Intelligence Surveillance Court, whose proceedings are secret.

Alexander said that more than 90 percent of the information on the foiled plots came from a program targeting the communications of foreigners, known as PRISM. The program was authorized under Section 702 of a 2008 law that amended the Foreign Intelligence Surveillance Act (FISA).

The law authorizes the NSA to collect e-mails and other Internet communications to and from foreign targets overseas who are thought to be involved in terrorism or nuclear proliferation or who might provide critical foreign intelligence. No American in the country or abroad can be targeted without a warrant, and no person inside the United States can be targeted without a warrant.

A second program collects all call records from U.S. phone companies. It is authorized under Section 215 of the USA Patriot Act. The records do not include the content of calls, location data, or a subscriber’s name or address. That law, passed in 2001 and renewed twice since then, also amended FISA.

Snowden, a high school dropout who worked at an NSA operations center in Hawaii for 15 months as a contractor, released highly classified information on both programs, claiming they represent government overreach. He has been in hiding since publicly acknowledging on June 9 that he leaked the material.

Several lawmakers pressed for answers on how Snowden, a low-level systems administrator, could have had access to highly classified material such as a court order for phone records.

“We need to seal this crack in the system,” said Rep. C.A. Dutch Ruppersberger (Md.), the ranking Democrat on the intelligence panel.

Alexander said he is working with intelligence officials to come up with a “two-person” rule to ensure that the agency can block unauthorized people from removing information from the system.

But Alexander and the other witnesses focused more heavily on justifying the programs and arguing that they operate under legal guidelines.

“As Americans, we value our privacy and our civil liberties,” Alexander said. “As Americans, we also value our security and our safety. In the 12 years since the attacks on September 11th, we have lived in relative safety and security as a nation. That security is a direct result of the intelligence community’s quiet efforts to better connect the dots and learn from the mistakes that permitted those attacks to occur on 9/11.”

Privacy protections

The officials described the privacy protections in detail.

Under Section 702, the NSA must destroy any data collected about U.S. persons — citizens or lawful permanent residents — that have nothing to do with foreign intelligence, a crime or terrorism, officials said. The agency may keep the data for five years and then must purge it.

Phone data are stored in a separate repository at the NSA that can be accessed by only 22 specially trained people, officials said.

A query can be made only if the analyst has “reasonable, articulable suspicion” that the phone number to be searched is associated with a specific terrorist organization, they said.

Both programs are subject to reporting requirements, though the reports are not public.

For instance, if there is a compliance problem — a wrong number is punched in — the error must be reported to the court immediately.

In addition, the Justice Department and the Office of the Director of National Intelligence conduct regular reviews and report to Congress and the courts on compliance.

Some lawmakers have raised doubts about just how critical Section 215 authority has been to foiling plots and asserted that much the same data may be obtained without amassing a government database of Americans’ call records.

Alexander said he was reviewing the feasibility of having the companies retain the records and conduct searches at government request.

The potential drawback, he said, is loss of agility in a crisis.