F.B.I. officials blamed an “apparent miscommunication” with the unnamed Internet provider, which mistakenly turned over all the e-mail from a small e-mail domain for which it served as host. The records were ultimately destroyed, officials said.

Bureau officials noticed a “surge” in the e-mail activity they were monitoring and realized that the provider had mistakenly set its filtering equipment to trap far more data than a judge had actually authorized.

The episode is an unusual example of what has become a regular if little-noticed occurrence, as American officials have expanded their technological tools: government officials, or the private companies they rely on for surveillance operations, sometimes foul up their instructions about what they can and cannot collect.

The problem has received no discussion as part of the fierce debate in Congress about whether to expand the government’s wiretapping authorities and give legal immunity to private telecommunications companies that have helped in those operations.

But an intelligence official, who spoke on condition of anonymity because surveillance operations are classified, said: “It’s inevitable that these things will happen. It’s not weekly, but it’s common.”

A report in 2006 by the Justice Department inspector general found more than 100 violations of federal wiretap law in the two prior years by the Federal Bureau of Investigation, many of them considered technical and inadvertent.

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