Osama bin Laden, Mr. Chertoff said, has made it clear that scaring the United States into an unsustainable spending spree is one of his aims. In a 2004 video, Mr. bin Laden, the Qaeda leader, spoke of “bleeding America to the point of bankruptcy.” “He understood that one tool he had in waging war against the United States was to drive us crazy, into bankruptcy, trying to defend ourselves against every conceivable threat,” Mr. Chertoff said at a hearing of the Homeland Security and Governmental Affairs Committee.

“We have to be realistic about what we expect and what we do. We do have limits, and we do have choices to make.” “I put my daughter in my car,” Mr. Chertoff told Mr. Lautenberg. “If I wanted my daughter to be 100 percent safe, I’d put a five-mile-an-hour speed limit cap on the car.” But that is not an option, he added, “because that’s more safety than we can afford.” The list of initiatives cannot be limitless, Mr. Chertoff said. A mandate, for example, that every cargo container headed into the United States be X-rayed and subject to a radiation scan before it leaves a foreign port to search for a possible nuclear bomb is not now feasible, he said. Senator Frank R. Lautenberg, Democrat of New Jersey, was trying on Tuesday to persuade him to consider such an effort.

The direct reference to Mr. bin Laden echoes what is now a week’s worth of tough talk by the Bush administration about him, a move Democrats call a politically motivated effort to refocus the nation, and its voters, on the war on terror instead of the troubled conflict in Iraq. Mr. Chertoff said his message was not political, but simply a recognition of reality and the tough choices he must make.