"America will be far safer if we reduce the chances of a terrorist attack in one of our cities than if we diminish the civil liberties of our own people"

The quote implies that Nancy Pelosi believes that it is more crucial to focus on preventing terrorist attacks from happening in cities within the United States than to restrict the civil liberties of American people in the name of security. She is suggesting that it is possible to maintain security and security without compromising the liberties and rights of individuals.