With little public debate, the N.S.A. has been undergoing rapid expansion in order to exploit the mountains of new data being created each day. The government has poured billions of dollars into the agency over the last decade, building a one-million-square-foot fortress in the mountains of Utah, apparently to store huge volumes of personal data indefinitely. It created intercept stations across the country, according to former industry and intelligence officials, and helped build one of the world’s fastest computers to crack the codes that protect information.

While once the flow of data across the Internet appeared too overwhelming for N.S.A. to keep up with, the recent revelations suggest that the agency’s capabilities are now far greater than most outsiders believed. “Five years ago, I would have said they don’t have the capability to monitor a significant amount of Internet traffic,” said Herbert S. Lin, an expert in computer science and telecommunications at the National Research Council. Now, he said, it appears “that they are getting close to that goal.”

On Saturday, it became clear how close: Another N.S.A. document, again cited by The Guardian, showed a “global heat map” that appeared to represent how much data the N.S.A. sweeps up around the world. It showed that in March 2013 there were 97 billion pieces of data collected from networks worldwide; about 14 percent of it was in Iran, much was from Pakistan and about 3 percent came from inside the United States, though some of that might have been foreign data traffic routed through American-based servers.

A Shift in Focus

The agency’s ability to efficiently mine metadata, data about who is calling or e-mailing, has made wiretapping and eavesdropping on communications far less vital, according to data experts. That access to data from companies that Americans depend on daily raises troubling questions about privacy and civil liberties that officials in Washington, insistent on near-total secrecy, have yet to address.

“American laws and American policy view the content of communications as the most private and the most valuable, but that is backwards today,” said Marc Rotenberg, the executive director of the Electronic Privacy Information Center, a Washington group. “The information associated with communications today is often more significant than the communications itself, and the people who do the data mining know that.”