They asked the Internal Revenue Service to examine his tax returns, but backed off after an I.R.S. employee suggested that Mr. Crow’s modest earnings would not impress a jury even if his returns were flawed. (He earns $32,000 a year at Ecology Action of Texas, he said.)

They infiltrated political meetings with undercover police officers and informers. Mr. Crow counts five supposed fellow activists who were reporting to the F.B.I.

Mr. Crow seems alternately astonished, angered and flattered by the government’s attention. “I’ve had times of intense paranoia,” he said, especially when he discovered that some trusted allies were actually spies.

“But first, it makes me laugh,” he said. “It’s just a big farce that the government’s created such paper tigers. Al Qaeda and real terrorists are hard to find. We’re easy to find. It’s outrageous that they would spend so much money surveilling civil activists, and anarchists in particular, and equating our actions with Al Qaeda.”

The investigation of political activists is an old story for the F.B.I., most infamously in the Cointel program, which scrutinized and sometimes harassed civil rights and antiwar advocates from the 1950s to the 1970s. Such activities were reined in after they were exposed by the Senate’s Church Committee, and F.B.I. surveillance has been governed by an evolving set of guidelines set by attorneys general since 1976.

But the Oklahoma City bombing in 1995 demonstrated the lethal danger of domestic terrorism, and after the Sept. 11 attacks, the F.B.I. vowed never again to overlook terrorists hiding in plain sight. The Qaeda sleeper cells many Americans feared, though, turned out to be rare or nonexistent.

Image Mr. Crow and an F.B.I. document he received under the Freedom of Information Act. Credit... Caleb Bryant Miller for The New York Times

The result, said Michael German, a former F.B.I. agent now at the American Civil Liberties Union, has been a zeal to investigate political activists who pose no realistic threat of terrorism.