An enemy detonates a nuclear weapon over the Pentagon. In four seconds, the blast wave reaches the Jefferson Memorial. It collapses in an instant. Scorching hot winds, at 300 miles an hour, scour every person and vehicle off the Memorial Bridge.

The fireball, bright as a thousand suns, quickly reaches the Capitol building. The structure shakes, yet stands. But inside, everything flammable -- from clothes to curtains -- bursts into flames.

Soon, 40 square miles are covered by roaring flames. Fingers of fire stretch as far as eight miles from the blast.

The D.C. area is home to 5.3 million people. All who haven't died within the first hour of the attack are in desperate need.

It's not a happy scenario. And Washington's doing nothing to improve it. In fact, President Obama plans to invest less, not more, in preparing our military to provide help in the wake of a catastrophic disaster on U.S. soil.

Defense Secretary Robert Gates promised the latest Quadrennial Defense Review would pay particular attention to homeland defense and the threat of catastrophic attack. Before the review came out, the military planned to have about 16,000 troops trained, ready and equipped to respond immediately to a homeland security crisis. The review reduced that number to about 13,000.

The Pentagon argues that less is actually more, because it has split the troops into smaller force packages that can get to a disaster area faster. But while smaller may be OK for small disasters, it won't work for big ones.

Most of the capability the Pentagon plans to add is "command and control" -- people who tell other people what to do. But that won't help much in catastrophic disasters involving chemical, biological, or radiological or nuclear attacks. The troops sent into the holocaust to work under them won't have the right training or the necessary special equipment.

Furthermore, it is unlikely that today's military could get there fast enough in big enough numbers to make a difference. In a catastrophic disaster, the first 72 hours are absolutely critical. Within that time, help must reach those with serious injuries, those in shock and those lacking water or shelter. If not, they die.

Studies by authorities such as the Rand Corp. and the congressionally chartered Commission on National Guard and Reserve suggest that the military actually needs tens of thousands more special forces trained and equipped to ameliorate catastrophes. These troops need strong working relationships with emergency responders across the nation and the ability to deploy on short notice.

Yet, the Pentagon is pitching for less, not more -- and the reason why is pretty simple. The entire review process was a rubber-stamp exercise forced to conform to budget decisions already made by -- or foisted on -- Gates.

This White House refuses to fund national security adequately. To pay for operations in Afghanistan and Iraq, Gates mortgaged the military's future capabilities -- including homeland defense.

This approach can be tragically penny-wise and pound-foolish. The price of unpreparedness can be staggering.

On Sept. 11, the U.S. lacked capacity to deal with ground zero in New York City. As a result, thousands of emergency responders, construction workers and good Samaritans rushed to the scene ill-prepared. Many were exposed to hazardous materials that cost them their health and may well cost taxpayers a bundle.

Recently, a judge rejected a legal settlement that would have paid out more than $575 million in compensation. The final bill for 9/11 could well exceed $5 billion. And 9/11 was not a catastrophic disaster.

James Jay Carafano is a senior research fellow for national security at the Heritage Foundation ( heritage.org).