SAN FRANCISCO — A federal judge has blocked the government from destroying telephone metadata collected by the National Security Agency that plaintiffs say is critical to suits challenging the constitutionality of the surveillance.

In a two-page order issued Monday, U.S. District Judge Jeffrey White of the Northern District of California granted an emergency motion from the Electronic Frontier Foundation to thwart the destruction of potential evidence in Jewel v. NSA, 08-4373, and First Unitarian Church of Los Angeles v. NSA, 13-3287, a pair of suits that object to the federal government’s harvesting of telephone call data.