IT IS TEMPTING to use the anniversary of Sept. 11, 2001, to list, once again, the local and national errors that led to the chaotic response to Hurricane Katrina two weeks ago. But to do so would be to repeat precisely the same mistake that Department of Homeland Security officials have made -- in response to demands from Congress and the public -- over the past four years. Put simply, this is a nation that is very good at fighting yesterday's battles, very good at distributing funds based on politics rather than risk and extraordinarily bad at fighting tomorrow's unexpected challenge.

Since Sept. 11, for example, there has been a large and extremely costly focus on airline security. Some $18 billion has been spent on the Transportation Security Administration over the past four years; in some years, its budget has exceeded that of the FBI. A good chunk of that money been wasted on bad contracts, awards banquets and undeserved bonuses. More important, the use of reinforced cockpit doors, and the doubtfulness of al Qaeda being able or willing to repeat another multiple airline hijacking, throws its very necessity in doubt.

At the same time, vast sums have been scattered far and wide on local projects, many also of doubtful necessity, simply because powerful members of Congress demanded them for their constituents. The truth is that there are entire states that don't need any homeland security funding at all. There are also some vulnerabilities that would be better dealt with locally, or even by the private sector. But instead of recognizing that reality, both houses of Congress have gone out of their way to ensure that everybody gets at least a small slice of the federal pie.

Meanwhile, neither DHS nor anyone else has focused hard enough on the major disasters for which the United States is still least prepared, namely a nuclear disaster or a biological attack, both of which would strain the nation's public health facilities way beyond capacity. It is still the case that far too little has been done to secure the nuclear and bioterrorism weapons of the former Soviet Union; that radiation testing is still not deployed with any precision at American ports; and that evacuation plans are, as became obvious this month, not geared to the immobile, not widely understood by either officials or by the public, and probably not feasible in many cases anyway.

Dealing with the biological threat, either from terrorists or a natural pandemic, will, in addition, require far larger federal government investment in biological science than this administration has yet been willing to make, as well as a far broader partnership with the pharmaceutical industry than anyone has yet been willing to contemplate. Work on finding vaccines and cures for existing diseases has just begun; ways for distributing vaccines in case of emergency have been contemplated in only a few places and instances; and the long-term investment in the technology that will be needed to anticipate and prevent new or engineered viruses has not yet been made.

Big disaster scenarios are, it is true, gloomy to contemplate. It is much easier for emergency planners and politicians to think about containable crises. It is also much easier for federal officials to respond automatically to local and congressional demands, rather than draw up their own risk-based and possibly unpopular plans. But if there is any point to having a department of homeland security, surely it is to think the unthinkable. And we see only slim evidence, so far, that DHS is engaged in that undertaking.