The requests for such data showed up a dozen times, using nearly identical language, in records from one six-month period in 2005 obtained by a nonprofit advocacy group, the Electronic Frontier Foundation, through a Freedom of Information Act lawsuit that it brought against the government. The F.B.I. recently turned over 2,500 pages of documents to the group. The boilerplate language suggests the requests may have been used in many of more than 700 emergency or “exigent” national security letters. Earlier this year, the bureau banned the use of the exigent letters because they had never been authorized by law.

The reason for the suspension is unclear, but it appears to have been set off in part by the questions raised by the inspector general’s initial review into abuses in the use of national security letters. The official said the F.B.I. itself was examining the use of the community of interest requests to get a better understanding of how and when they were used, but he added that they appeared to have been used in a relatively small percentage of the tens of thousand of the records requests each year. “In an exigent circumstance, that’s information that may be relevant to an investigation,” the official said.

A federal judge in Manhattan last week struck down parts of the USA Patriot Act that had authorized the F.B.I.’s use of the national security letters, saying that some provisions violated the First Amendment and the constitutional separation of powers guarantee. In many cases, the target of a national security letter whose records are being sought is not necessarily the actual subject of a terrorism investigation and may not be suspected at all. Under the Patriot Act, the F.B.I. must assert only that the records gathered through the letter are considered relevant to a terrorism investigation.

Some legal analysts and privacy advocates suggested that the disclosure of the F.B.I.’s collection of community of interest records offered another example of the bureau exceeding the substantial powers already granted it by Congress.

“This whole concept of tracking someone’s community of interest is not part of any established F.B.I. authority,” said Marcia Hofmann, a lawyer for the Electronic Frontier Foundation, which provided the records from its lawsuit to The New York Times. “It’s being defined by the F.B.I. And when it’s left up to the F.B.I. to decide what information is relevant to their investigations, they can vacuum up almost anything they want.”

Matt Blaze, a professor of computer and information science at the University of Pennsylvania and a former researcher for AT&T, said the telecommunications companies could have easily provided the F.B.I. with the type of network analysis data it was seeking because they themselves had developed it over many years, often using sophisticated software like a program called Analyst’s Notebook.

“This sort of analysis of calling patterns and who the communities of interests are is the sort of things telephone companies are doing anyway because it’s central to their businesses for marketing or optimizing the network or detecting fraud,” said Professor Blaze, who has worked with the F.B.I. on technology issues.