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“It raises some legitimate legal questions and some legitimate privacy issues,” he said.

Officials have said the information is collected, but that the FISA court must approve any searches of the data, which are used to detect communications that foreign terrorists might have with people in the United States.

Mr. Baker said the intelligence agencies traditionally had gone to court to ask for permission to gather such data — “authorization first, then collection.”

“But if you know you are going to need to do searches of this very large data set, why not collect it first, then get court approval for whatever searches you want to do?” he said. “The net effect is the same.”

On Monday, Mr. Greenwald of The Guardian promised more revelations.

“We do have more big stories coming, without question,” he told CNN.