Napolitano spoke Wednesday in New York City at the Council on Foreign Relations before heading to ground zero.
She said the public has been treated as a "liability to be protected," instead of an asset in maintaining the nation's security.
Americans, she says, have a role along with local law enforcement, the federal government and the international community. She urged people to prepare their families, volunteer, get free training and join local emergency response teams.
Napolitano also meets Wednesday with counterterrorism experts and law enforcers at the Staten Island Ferry Terminal. A transportation security announcement is planned at Grand Central Terminal.