Now that the metadata programme has been declassified, he can openly correct that error, he wrote in a letter to Feinstein. The letter dated June 21 was released to the press on Tuesday.
"My response was clearly erroneous - for which I apologize," he said.
"While my staff acknowledged the error to Senator Wyden's staff soon after the hearing, I can now openly correct it because the existence of the metadata collection program has been declassified," Clapper said.
Before the secretive internet and telephone surveillance programme was leaked, Clapper told the lawmakers during Congressional hearing that the National Security Agency does not collect data on millions of Americans.
Clapper said he is now writing because of the "charged rhetoric and heated controversy" over his response, so he could "set the record straight."