Lawmakers say their votes to restrain the N.S.A. reflect a gut-level concern among voters about personal privacy.

“I represent a very reasonable district in suburban Philadelphia, and my constituents are expressing a growing concern on the sweeping amounts of data that the government is compiling,” said Representative Michael G. Fitzpatrick, a moderate Republican who represents one of the few true swing districts left in the House and who voted on Wednesday to limit N.S.A. surveillance.

Votes from the likes of Mr. Fitzpatrick were not initially anticipated when Republican leaders chided reporters for their interest in legislation that they said would go nowhere. As the House slowly worked its way on Wednesday toward an evening vote to curb government surveillance, even proponents of the legislation jokingly predicted that only the “wing nuts” — the libertarians of the right, the most ardent liberals on the left — would support the measure.

Then Mr. Sensenbrenner, a Republican veteran and one of the primary authors of the post-Sept. 11 Patriot Act, stepped to a microphone on the House floor. Never, he said, did he intend to allow the wholesale vacuuming up of domestic phone records, nor did his legislation envision that data dragnets would go beyond specific targets of terrorism investigations.