By Tabassum Zakaria and Warren Strobel

FORT MEADE, Maryland (Reuters) - The U.S. National Security Agency has made dozens of changes in its operations and computer networks to prevent the emergence of another Edward Snowden, including potential disciplinary action, a top NSA official said on Friday, as a White House review panel recommended restraints on NSA spying.

Former NSA contractor Snowden's disclosures have been "cataclysmic" for the eavesdropping agency, Richard Ledgett, who leads a task force responding to the leaks, said in a rare interview at NSA's heavily guarded Fort Meade headquarters.

In the more than hour-long interview, Ledgett acknowledged the agency had done a poor job in its initial public response to revelations of vast NSA monitoring of phone and Internet data; pledged more transparency; and said he was deeply worried about highly classified documents not yet public that are among the 1.7 million Snowden is believed to have accessed.

He also stoutly defended the NSA's mission of tracking terrorist plots and other threats, and said its recruiting of young codebreakers, linguists and computer geeks has not been affected by the Snowden affair - even as internal morale has been.

"Any time you trust people, there is always a chance that someone will betray you," he said.

The NSA is taking 41 specific technical measures to control data by tagging and tracking it, to supervise agency networks with controls on activity, and to increase oversight of individuals.

Measures include requiring two-person control of every place where someone could access data and enhancing the security process that people go through and requiring more frequent screenings of systems administrative access, Ledgett said.

After months of sometimes blistering criticism in the news media and by Congress and foreign governments, the publicity-averse NSA is now mounting an effort to tell its side of the Snowden story.

It granted access to NSA headquarters to a team from CBS' "60 Minutes" program, which is scheduled to broadcast a segment on the agency on Sunday.

Ledgett, a 36-year intelligence veteran who reportedly is in line to be the agency's deputy director, joked that doing media interviews was "a complete out-of-body experience for me."

He spoke to Reuters on the same day that the White House said it had decided to maintain the practice of having a single individual head both the NSA and U.S. Cyber Command, which conducts cyberwarfare - an outcome the NSA leadership favored.

Separately, news reports late Thursday said an outside review panel appointed by the White House has recommended changes in a program disclosed by Snowden that collects basic data on Americans' phone calls - known as metadata.

The panel reportedly said the data should be held by an organization other than the NSA and stricter rules should be enforced for searching the databanks.

Ledgett declined to discuss the panel's specific recommendations. But he seemed to acknowledge that tighter guidelines for NSA eavesdropping were in the offing, saying that what is technologically possible "has gotten ahead of policy."

Snowden, who is living under asylum in Russia, disclosed a vast U.S. eavesdropping apparatus that includes the phone metadata program; NSA querying of Internet communications via major companies such as Google Inc (GOOG.O) and Facebook Inc (FB.O); and widespread tapping of international communication networks.

Ledgett made no apologies for what many see as overly aggressive NSA monitoring. He noted that the U.S. government's intelligence taskings to the agency run to 36,000 pages, and said its activities take place within a "box" of U.S. laws and policies.

"We'll color in every square millimeter of that box," he said, implying the NSA will use its legal authorities to the fullest extent possible.

The NSA's internal review has determined about 98 percent of the scope of the material that Snowden had accessed, and officials have found no evidence that he had help either within the NSA or from adversary spy agencies.

Ledgett said that when Snowden was downloading the documents, NSA was ahead of other intelligence agencies in installing "insider threat" software that President Barack Obama ordered in the wake of an earlier leak scandal involving the group WikiLeaks. But installation of the software, which might have stopped Snowden, was not complete.

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