WASHINGTON — A federal study released on Thursday concluded that there was no effective alternative to the government’s “bulk collection” of basic information about every telephone call made in the United States, a practice that civil rights advocates call overly intrusive.

Last year, after the former intelligence contractor Edward J. Snowden revealed details of the government’s vast data-collection enterprise, President Obama asked intelligence agencies to assess whether there was a way to get at the communications of terrorism suspects without sweeping up records of all calls made and received inside the United States, including their length and other identifying information.

On Thursday, the National Academy of Sciences, in a detailed report that brought together communications and cybersecurity experts and former senior intelligence officials, said that “no software-based technique can fully replace the bulk collection of signals intelligence.” But it also concluded that there were ways to “control the usage of collected data” and to make sure that once it is in the government’s hands, there are stronger privacy protections.

The findings came a year after Mr. Obama announced modest reforms to practices of the National Security Agency that had been revealed by Mr. Snowden, including doing away with a huge government-run database of phone records and instead relying on separate databases managed by phone companies.