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No intelligence reports had been produced based on the illegal checks, the officials said. They described the alert list as “an analytic tool” and “a way that NSA tried to prioritize its work,” rather than an intelligence-gathering tool.

“We were focused on the archive, as was the court,” said the official, referring to the massive five-year database.

That was one reason the violations took so long to come to light, the official said.

Tuesday’s disclosures are likely to add to pressure on the administration over the Section 215 program and other broad domestic data-gathering by the NSA. The House narrowly failed to delete funding for the program earlier this summer in a vote that came shockingly close for many in U.S. intelligence world.

One of the authors of the Patriot Act — hurriedly passed by Congress after the Sept. 11, 2001, terrorist attacks on the United States — said last week that Section 215 was never intended to be used in this fashion.

Wisconsin Republican F. James Sensenbrenner Jr., who was chairman of the House Judiciary Committee at the time the act passed, joined a legal challenge by the Electronic Frontier Foundation to the constitutionality of the NSA’s use of Section 215.

The lawsuit has also been joined by many other groups, including recently the National Rifle Association and a Jewish social-justice organization called the Shalom Center.

For two years, the foundation has been embroiled in another case about the 215 program in a lawsuit under the U.S. Freedom of Information Act.

The administration “may attempt to portray [the release of the documents] as being done out of the goodness of its heart and as a testament to its commitment to transparency,” argued the Electronic Frontier Foundation’s Trevor Timm on its blog. But, he said the Justice Department released this information because a court ordered the disclosure in response to the foundation’s lawsuit.

Mr. Timm said that the department fought “tooth and nail to keep every page of its interpretations secret, even once arguing it should not even be compelled to release the number of pages that their opinions consisted of.”