After Sept. 11, the administration worked to prevent another jet from slamming into a skyscraper. Hurricane Rita demonstrated that President Bush would not abide another Katrina.

The essence of emergency preparedness, though, lies not in the ability to cope with the last disaster but in mitigating the next one. Though predicting catastrophes is difficult, one looms large: a bird-flu pandemic.

During his summer siesta, the president reportedly read a book chronicling the 1918 flu epidemic, and his recent address to the United Nations contained a line addressing the issue. Both are hopeful signs, but our preparations for what may come are already woefully inadequate.

Imagining what might lie ahead is not easy. We are used to flu season as a relatively minor irritant; senior citizens need a shot and the rest of us try to avoid being bedridden for a week. There is about as much relationship between that scene and a bird-flu pandemic as there is between a rifle shot and a nuclear explosion.

For Americans, the 1918 flu epidemic began in a Kansas army camp. Within three months, 43,000 U.S. military personnel had died. All told, 675,000 Americans succumbed, the equivalent of 2 million today. Worldwide, 50 million to 100 million people perished.

Bird flu is likely to be much worse, first because this particular viral combination has never before spread among humans. Thus no one has developed any immunity; everyone is susceptible. Second, this flu is extraordinarily deadly. The 1918 flu killed only about 3 percent of the people it infected. This one has killed 50 percent of those infected thus far.

Even if its virulence is cut in half, the carnage will be unparalleled — potentially 16 million deaths in the United States, hundreds of millions worldwide.

The resulting economic devastation and political instability will be unique in human history. After 700 people died of SARS, travel to Asia abruptly stopped for months while trade was slashed. Imagine what will happen if millions start dying. People and products will be quarantined, trade will grind to a halt, governments will be destabilized. An Oxford University team puts the cost of a low-level epidemic at $2 trillion to $3 trillion, noting that the costs of a highly virulent strain are incalculable.

Got your attention yet?

Of course, it may not happen. To date, we’ve been saved by the failure of the virus to develop a mechanism for human-to-human transmission. Most scientists believe it is only a matter of time until that mutation occurs. A recent World Health Organization report concluded that the “risk is great. … During 2005 ominous changes have been observed in the virulence of the disease.”

How prepared are we? With the world’s limited vaccine-production capacity, it is likely that just 14 percent of the world’s population will receive shots within a year — 100 percent will need them.

Another potentially effective medication is Tamiflu. Because the United States got in line late for the Swiss drug, we have only about 2 million doses. Australia has 3.5 million, while the United Kingdom says it has enough to cover a quarter of its population.

Then there is treatment for those who get sick. Right now, the United States has about 105,000 mechanical ventilators. Hundreds of thousands will be needed within weeks of an outbreak.

This catalog of horrors only scratches the surface, and we have not begun to grapple with the tough questions. Will we risk shipping some of our precious vaccine to Asia in an effort to stop the pandemic before it spreads? What, who and how will we quarantine? Who will get our limited supply of shots and Tamiflu?

Catastrophes of this magnitude seem inconceivable. A few weeks ago, the destruction of an entire American city was also inconceivable. While we are rebuilding from the last catastrophe, let’s remember to prevent the next one.

Mellman is president of The Mellman Group and has worked for Democratic candidates and causes since 1982, including Sen. John Kerry (D-Mass.) last year.