Armitage said the revelation of Plame's identity, which triggered an investigation into the leak, was inadvertent, CNN reported Friday.
"I feel terrible," Armitage told CBS News. "Every day, I think, I let down the president. I let down the secretary of state. I let down my department, my family, and I also let down Mr. and Mrs. Wilson."
Novak had revealed in a July 14, 2003, column that Plame, wife of former diplomat and Iraq war intelligence critic Joe Wilson, was a CIA operative. Novak cited two senior administration officials, one of which was later revealed to be Karl Rove, U.S. President George Bush's chief political strategist.
Novak, who said he would not reveal the name of his first source until he came forward on his own, said Rove had confirmed the information.
Armitage said Plame's role in the CIA was mentioned in casual conversation.