THE BUSH administration, pertinent congressional committees and the D.C. government are all aware of a study showing that an attack on a single railroad tank car of chlorine traveling through a crowded nation's capital could:

* Kill or seriously harm 100,000 people within an hour.

* Set off a toxic plume that could extend over 40 miles.

* Leave deadly a core area of about 4 miles by 141/2 miles.

It is also true that while the D.C. government has enacted a law to deal with the issue, the federal government has taken no serious steps to prevent chemicals that are toxic if inhaled from being shipped through the District. What's more, the Justice Department and CSX Transportation Inc., rather than supporting D.C. legislation that sought to regulate the transport of ultra-hazardous materials through the city, instead obtained a court order to stop the District from enforcing its law.

As a result of federal opposition to local efforts, an undisputed risk to life and safety in the Washington region is unabated. Credit D.C. Council member Kathy Patterson (D-Ward 3) with bringing this danger to the public's attention and for marshaling legislative support on the council for a solution -- "to reduce the risk of an attack by removing the target from our midst," as she told the Department of Homeland Security in a letter yesterday. Again, Mrs. Patterson was putting her finger on the problem.

Mrs. Patterson was responding to a proposed Department of Homeland Security rail security plan that aims to protect city residents by installing surveillance cameras along seven miles of CSX Transportation tracks. She noted that the cameras "would, surely, provide historical documentation of what vehicle or what individuals gained sufficient proximity to the CSX tracks to blow up a 90-ton tanker full of chlorine -- after the fact of thousands of deaths." She rightly notes that the Homeland Security plan would not prevent a suicide bomber from accessing the tracks. It would only record the bomber doing the dastardly deed. Hooray.

Residents, visitors, members of Congress and the Supreme Court deserve better. They need a federal plan that prevents, rather than simply detects, an attack on the city. On that score, nothing less than rerouting ultra-hazardous materials -- dangerous, toxic-by-inhalation cargo -- around densely populated communities at high risk of attack, such as the nation's capital, will do. Alternative routes for such chemicals are needed here in the District and for other high-risk communities around the nation. The difficulty of the challenge is no reason for the federal government to avert its gaze from this potential nightmare. It must either step up to the problem now or try to explain away the poor federal planning for a catastrophe in yet another national disaster's after-action report.