Administration Says Mining of Data Is Crucial to Fight Terror

WASHINGTON — In early September 2009, an e-mail passed through an Internet address in Peshawar, Pakistan, that was being monitored by the vast computers controlled by American intelligence analysts. It set off alarms. The address, linked to senior Qaeda operatives, had been dormant for months.

Investigators worked their way backward and traced the e-mail to an address in Aurora, Colo., outside Denver. It took them to Najibullah Zazi, a 24-year-old former coffee cart operator, who was asking a Qaeda facilitator about how to mix ingredients for a flour-based explosive, according to law enforcement officials. A later e-mail read: “The marriage is ready” — code that a major attack was planned.

What followed in the next few days was a cross-country pursuit in which the police stopped Mr. Zazi on the George Washington Bridge, let him go, and after several false starts, arrested him in New York. He eventually pleaded guilty to plotting to carry out backpack bombings in the city’s subway system.

It is that kind of success that President Obama seemed to be referring to on Friday in California when he defended the National Security Agency’s stockpiling of telephone call logs of Americans and gaining access to foreigners’ e-mail and other data from Microsoft, Google, Yahoo and other companies.

He argued that “modest encroachments on privacy” — including keeping records of phone numbers called and the length of calls that can be used to track terrorists, though not listening in to calls — were “worth us doing” to protect the country. The programs, he said, were authorized by Congress and regularly reviewed by federal courts.

But privacy advocates questioned the portrayal of the program’s intrusion on Americans’ communications as modest. When Americans communicate with a targeted person overseas, the program can vacuum up and store for later searching — without a warrant — their calls and e-mails, too.

Mr. Obama acknowledged that he had hesitations when he inherited the program from George W. Bush, but told reporters that he soon became convinced of its necessity. “You can’t have 100 percent security and also then have 100 percent privacy and zero inconvenience,” he said. “We’re going to have to make some choices as a society.”

To defenders of the N.S.A., the Zazi case underscores how the agency’s Internet surveillance system, called Prism, which was set up over the past decade to collect data from online providers of e-mail and chat services, has yielded concrete results.

“We were able to glean critical information,” said a senior intelligence official, who spoke on the condition of anonymity. “It was through an e-mail correspondence that we had access to only through Prism.”

John Miller, a former senior intelligence official who now works for CBS News, said on “CBS This Morning,” “That’s how a program like this is supposed to work.”

Veterans of the Obama intelligence agencies say the large collections of digital data are vital in the search for terrorists. “If you’re looking for a needle in the haystack, you need a haystack,” Jeremy Bash, chief of staff to Leon E. Panetta, the former C.I.A. director and defense secretary, said on MSNBC on Friday.

Under the program, intelligence officials must present Internet companies with specific requests for information on a case-by-case basis, showing that the target is a foreigner and located outside the United States, a senior law enforcement official said Friday. If the N.S.A. comes across information about an American citizen during the search, it turns over that material to the F.B.I. for an assessment, the official said.

An administration official said Friday that agencies were evaluating whether they could publicly identify particular terrorism cases that came to the government’s attention through the telephone or Internet programs.

Representative Mike Rogers, the Michigan Republican who is chairman of the House intelligence committee, said Thursday that the phone program “was used to stop a terrorist attack.” He did not identify the plot, or explain whether the call logs in the case would have been unavailable by ordinary subpoenas.

Two Democratic senators on the Intelligence Committee who have been warning about the bulk collection of records under the Patriot Act, Ron Wyden of Oregon and Mark Udall of Colorado, said Friday that their study of the calling log program has convinced them that it was not worth its cost to privacy.

Mark Mazzetti and Michael S. Schmidt contributed reporting.