Those comments were prompted by a document in the Snowden trove that said the United States conducted more than 200 offensive cyberattacks in 2011 alone. But American officials say that in reality only a handful of attacks have been carried out. They say the erroneous estimate reflected an inaccurate grouping of other electronic missions.

But General Alexander would not discuss any specific cases in which the United States had used those weapons, including the best-known example: its years-long attack on Iran’s nuclear enrichment facility at Natanz. To critics of President Obama’s administration, that decision made it easier for China, Iran and other nations to justify their own use of cyberweapons.

General Alexander, who became the N.S.A. director in 2005, will retire early next year. The timing of his departure was set in March when his tour was extended for a third time, according to officials, who said it had nothing to do with the surveillance controversy spawned by the leaks. The appointment of his successor is likely to be a focal point of Congressional debate over whether the huge infrastructure that was built during his tenure will remain or begin to be restricted.

Senator Patrick J. Leahy, a Vermont Democrat who leads the Senate Judiciary Committee, has already drafted legislation to eliminate the N.S.A.’s ability to systematically obtain Americans’ calling records. And Representative Jim Sensenbrenner, a Wisconsin Republican and co-author of the Patriot Act, is drafting a bill that would cut back on domestic surveillance programs.

General Alexander was by turns folksy and firm in the interview. But he was unapologetic about the agency’s strict culture of secrecy and unabashed in describing its importance to defending the nation.

He insisted that it would have been impossible to have made public, in advance of the revelations by Mr. Snowden, the fact that the agency collected what it calls the “business records” of all telephone calls, and many other electronic communications, made in the United States. The agency is under rules preventing it from investigating that so-called haystack of data unless it has a “reasonable, articulable” justification, involving communications with terrorists abroad, he added.

But he said the agency had not told its story well. As an example, he said, the agency itself killed a program in 2011 that collected the metadata of about 1 percent of all of the e-mails sent in the United States. “We terminated it,” he said. “It was not operationally relevant to what we needed.”