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Other surveys have found a steady decline in the president’s popularity in his second term. An NBC News/Wall Street Journal poll in early June showed that Mr. Obama’s approval rating had dipped to 48 percent, from 53 percent in December. A CBS/New York Times survey showed his job approval at 47 percent at the start of this month, down from 51 percent in early January.

The CNN poll revealed that Americans are more evenly split on the need for aggressive snooping efforts such as those conducted by the NSA and other intelligence agencies.

A slim majority said the Obama administration has been about right (38 percent) or has not gone far enough (17 percent) in balancing restrictions on civil liberties to fight terrorism, while 51 percent approve of the NSA program to gather phone records.

Snowden speaks

Mr. Snowden contended in his online session that there are few safeguards to prevent abuse of data-gathering projects and that large amounts of data about Americans routinely are collected in dragnet searches, despite officials’ denials.

“The reality is this [any U.S. intelligence agency] has access to query raw databases, they can enter and get results for anything they want. Phone number, email, user id, cell phone handset ID, and so on,” he said. “The restrictions against this are policy-based, not technically based,” Mr. Snowden added.

Even though U.S. intelligence officials note that the warrantless monitoring of U.S. citizens’ communications is illegal, he said, “Americans’ communications are collected and viewed on a daily basis on the certification of an analyst rather than a warrant.”

Officials “excuse this as ‘incidental’ collection, but at the end of the day, someone at NSA still has the content of your communications,” he said. “If I target for example an email address and that email address sent something to you, Joe America, the analyst gets it. All of it. [Internet protocols], raw data, content, headers, attachments, everything. And it gets saved for a very long time.”

Mr. Snowden, whom some lawmakers have called a traitor, also charged that audits to check for misuse “are cursory, incomplete, and easily fooled by fake justifications.”

He said for the British electronic espionage agency, General Communications’ Headquarters, or GCHQ, only 5 percent of queries performed were audited.

Mr. Snowden also denied disclosing legitimate NSA operations when he spoke to an English-language Chinese newspaper about the agency’s hacking of computer systems in China and in Hong Kong, where he fled with a thumb drive containing “dozens” of agency secrets.

“I did not reveal any U.S. operations against legitimate military targets,” he said of his interview last week with the South China Morning Post. “I pointed out where the NSA has hacked civilian infrastructure such as universities, hospitals and private businesses because it is dangerous. Not only that, when NSA makes a technical mistake during an exploitation operation, critical systems crash.”

He said many of the operations he was planning to expose, including electronic and Web-based eavesdropping on foreign diplomats at a Group of 20 summit in 2009 revealed Monday, were directed against friendly countries.

“Congress hasn’t declared war on the countries — the majority of them are our allies — but without asking for public permission, NSA is running network operations against them that affect millions of innocent people.”