We don’t know exactly what information the National Security Agency has ceased collecting , and we don’t know what legal issue persuaded which judge that collecting it was a problem. But the Washington Post tells us that there will be a hiatus for some time in the surveillance of terrorist communications. If it should happen that they are able to exploit this particular security gap, we will probably one day learn just who was responsible.

A special federal court that oversees domestic surveillance has raised concerns about the National Security Agency’s collection of certain types of electronic data, prompting the agency to suspend collecting it, U.S. officials said.

The Foreign Intelligence Surveillance Court, which grants orders to U.S. spy agencies to monitor U.S. citizens and residents in terrorism and espionage cases, recently “got a little bit more of an understanding” about the NSA’s collection of the data, said one official, who spoke on the condition of anonymity because such matters are classified.

The data under discussion are records associated with various kinds of communication, but not their content. Examples of this “metadata” include the origin, destination and path of an e-mail; the phone numbers called from a particular telephone; and the Internet address of someone making an Internet phone call. It was not clear what kind of data had provoked the court’s concern.

Some House Republicans have argued that the suspension of collection creates an intelligence gap that undermines the government’s ability to track and identify terrorist networks, according to officials familiar with the matter. Frustrated about waiting for a remedy, these Republicans say the gap can be closed with a technical fix to the Foreign Intelligence Surveillance Act, the officials said.

“This is a basic tool we used to have, and it’s now gone,” said one intelligence official familiar with the impasse. “Every day, every week that goes by, there’s just one more week of information that we’re not collecting. You sit there and say, ‘This is unbelievable that we have this gap.’ ”

The data could be used to help analysts learn whom a suspect was working and communicating with, and to “detect and anticipate” a plot, the official said. “It’s not a concern over what was being collected,” he said. “It’s just a question about whether the law was written in a way that allowed the information to be collected in a way that they were collecting it.” …

The NSA voluntarily stopped gathering the data in December or January rather than wait to be told to do so, the officials said. The agency had been collecting it with court permission for several years, officials said.