Washington ? Pulling all troops from Iraq too soon could spawn a “failed state” that terrorists use to attack America, just like Afghanistan, Sen. Hillary Clinton said Thursday.

“We made this mistake before,” Clinton, D-N.Y., told the New York Daily News, defending her plan to keep some soldiers in Iraq if she becomes president.

“We withdrew from Afghanistan after basically funding and creating the mujahedeen, including (Osama) bin Laden,” she said. “We walked out, and we left a failed state that came back and killed all those people in our city.”

Clinton has been campaigning aggressively against President Bush’s troop escalation, pledging to “extricate” America if she is elected.

But she found herself on the defensive with anti-war activists Thursday after The New York Times highlighted an interview in which she said she’d leave some U.S. troops in Iraq, north of Baghdad, to fight al-Qaida.

“That kind of sounds like the Republicans saying if we don’t fight them over there, we’ll fight them here,” said Sue Udry, of United for Peace and Justice. “Think about the ethics of that. Al-Qaida wasn’t there before we were, and after we came, thousands of civilians are getting killed.”

Clinton said Thursday she didn’t know how big a force would be needed, but downplayed the size, and said the idea is part of the Democrats’ approach to ending the war. Her main rival, Sen. Barack Obama, D-Ill., also has said he would leave U.S. forces behind to fight al-Qaida.

Clinton, who has refused to apologize for her vote authorizing the war, said the number of troops left after 2009 would depend on how well al-Qaida is kept in check, whether Iran is meddling and how well the Iraqis do for themselves.

“We can’t walk away from that,” she said. “I don’t know anybody who has looked at this from a military perspective who says that we would need a lot of troops to keep that up. We’re talking mostly Special Forces.”