One week after the bombings on London's subway and bus systems, Chertoff said the U.S. government is bound to financially support the security of the nation's commercial airlines in part because the aviation system is almost exclusively a federal responsibility.
By contrast, he said, U.S. mass transit systems are largely owned and operated by state and local authorities. He also said the federal government must focus on attacks that could produce the most casualties.
"The truth of the matter is, a fully loaded airplane with jet fuel, a commercial airliner, has the capacity to kill 3,000 people," Chertoff told Associated Press reporters and editors. "A bomb in a subway car may kill 30 people. When you start to think about your priorities, you're going to think about making sure you don't have a catastrophic thing first."
Asked if this meant communities should be ready to provide the bulk of the protection for local transit systems, Chertoff said, "Yep."
State and local officials are grappling with how to pay for upgrades to protect commuters and other mass transit riders in their communities. Technology to protect mass transit systems in the nation's 30 largest metropolitan areas could cost an estimated $6 billion, according to industry representatives.
A Senate fight is looming this week among ranking Republicans who differ on how much to spend on mass transit security. A GOP-written bill financing the Homeland Security Department for next year would provide $100 million, but some Republicans want to boost that to $1.1 billion.
Chertoff drew a comparison between lifestyles and attitudes in the United States and Europe that he said play a part in preventing terror attacks.