One part of the program is called Upstream. It involves the collection of emails and other Internet messages as they cross network switches. The report discusses how network providers are legally compelled to give the N.S.A. communications “related to tasked selectors.” A little later, after a redacted paragraph, it says, “The providers should deliver only communications meeting these criteria to N.S.A.”

And the report said that “for each source of collection, N.S.A. employs processes to determine whether” — the middle of the sentence is redacted, before it picks up with, “are sending communications only for selectors currently tasked and authorized for collection.”

A senior administration official, speaking on the condition of anonymity to discuss internal deliberations, said there had been no official policy decision, as part of disclosing the inspector general report, to say more about how Upstream collection works than what the government had said previously.

Still, in previous reports and court documents about the Upstream system, the government has tended to use language that leaves it ambiguous whether the telecommunications companies or the government is filtering and scanning the raw Internet data.

(The inspector general report does not address how the N.S.A. collects foreign-to-foreign Internet messages passing through the American network. Such messages are not protected by domestic law, and the government does collect them in bulk, just as it could do if it intercepted them abroad, according to leaked documents and officials familiar with that system.)

The new report’s discussion of how the Upstream collection system works under the FISA Amendments Act dovetails with an article by The Times and ProPublica in August, which was largely based on “top-secret” documents provided by Mr. Snowden. But those documents remain classified. And in public, the government has been vague about the system’s details, including in its responses to lawsuits.

The cases are important because Internet technology works differently from the telephone technology for which wiretapping rules were developed and tested in court. A suspect’s phone call can be intercepted without touching any other people’s calls. But on the Internet, data from different messages are broken up and intermingled, so collecting a suspect’s email requires temporarily copying and sifting data from many people’s messages.