WASHINGTON — The Obama administration tried Saturday to marshal new evidence in defense of its collection of private Internet and telephone data, arguing that a secret program called Prism is simply an “internal government computer system” designed to sort through court-supervised collection of data, and that Congress has been briefed 13 times on the programs since 2009.

After rushing to declassify some carefully selected descriptions of the programs, James R. Clapper Jr., the director of national intelligence, conceded for the first time that the Prism program existed. But in a statement, after denouncing the leak of the data to The Guardian and The Washington Post, Mr. Clapper insisted it was “not an undisclosed collection or data mining program.” Instead, he said it was a computer system to “facilitate” the collection of foreign intelligence that had been authorized by Congress.

Mr. Clapper also insisted that the government “does not unilaterally obtain information from the servers” of telephone and Internet providers, saying that information is turned over only under court order, when there is a “documented, foreign intelligence purpose for acquisition” of the data.

He appeared to be attempting to push back against early reports that the government had direct access to the huge computer servers at Google, Microsoft, Facebook and similar companies. Those firms have denied they give the government a “back door” to their systems.