Armitage's acknowledgment Sunday came in response to comments by Valerie Plame, who said the former Bush administration official had no right to talk to a reporter about where she worked.
A year ago, Armitage publicly apologized to Plame and her husband. The former No. 2 State Department official remains the only principal in the leak to have done so.
At least three one-time administration officials in addition to Armitage discussed Plame's CIA status with reporters. They are former White House political adviser Karl Rove, Vice President Dick Cheney's ex-chief of staff, I. Lewis "Scooter" Libby and former presidential press secretary Ari Fleischer.
Armitage and Rove were the sources for a 2003 newspaper column by conservative commentator Robert Novak that disclosed Plame's CIA employment.
Novak's column came out eight days after Plame's husband, Joseph Wilson, said the administration had twisted prewar intelligence to exaggerate the Iraqi threat.
Libby was convicted this year of perjury, obstruction of justice and lying to the FBI about his conversations with reporters regarding Plame.
After receiving immunity from prosecution, Fleischer admitted to a federal grand jury that he had told reporters about Plame.
President George W. Bush, who was questioned in the criminal investigation, originally said that he would fire anyone in his administration who was involved in leaking Plame's name.
Instead, he commuted Libby's 30-month prison sentence, and never took any individual to task publicly for the leak.
In July, the president said the criminal investigation had run its course and that "now we're going to move on."
Armitage has taken a different tack.
"I think it was extraordinarily foolish of me" to have disclosed Plame's identity, Armitage said Sunday on CNN's "Late Edition." He was agreeing with comments by Plame that he should have known better.
Armitage said there was no ill-intent on his part. He said he spoke to Novak after seeing a reference to Wilson's wife in a memo.
The fact that she was named in a memo, Armitage said, led him to assume that she was not a covert employee, because he'd never seen, in 43 years with a security clearance, a covert operative's name in a memo.
"It was foolish, yeah," he said.
Plame sued Cheney, Rove, Libby and Armitage for alleging violating her rights, but a federal judge dismissed the case, saying there was no legal basis for it.
Despite the dismissal, the judge said the lawsuit raised important questions relating to the propriety of actions undertaken by the highest U.S. government officials.