The department has been working for a year on a National Planning Scenarios plan that outlines a number of plausible attacks _ including by nerve gas, anthrax, pneumonic plague and truck bomb.
The report, still confidential, was requested by a presidential directive in December 2003 and will be made public in upcoming months, Homeland Security spokesman Brian Roehrkasse said Tuesday. It was inadvertently posted on Internet sites of several states, including Hawaii, before it was taken down, Roehrkasse said. The other states were not immediately identified.
Homeland Security ''has developed a number of scenarios that will aid federal, state and local homeland security officials in developing plans to become more prepared to prevent and respond to an act of terrorism, should it occur,'' Roehrkasse said.
The plan also ''will help us better target our efforts and resources in improving the nation's preparedness,'' he said.
Officials said there was no credible indication that such specific attacks were being planned.
The draft plan was first reported Tuesday night on the Internet site of The New York Times.
The report does not hypothesize where such attacks would take place, Roehrkasse said. ''The overall goal is to increase the overall baseline preparedness of all states and cities throughout the country,'' he said.
Besides identifying possible types of attacks, Roehrkasse said the report also estimates how many deaths and amount of economic damage the attacks would cause.
According to the Times, they include:
_Blowing up a chlorine tank, killing 17,500 people and injuring more than 100,000.
_Spreading pneumonic plague in the bathrooms of an airport, sports arena and train station, killing 2,500 and sickening 8,000 worldwide.
_Infecting cattle with foot and mouth disease in several places, resulting in hundreds of millions of dollars in losses.
But a nuclear bomb, an exploding liquid chlorine tank or a widespread and prolonged aerosol anthrax spray ranked among the most devastating attacks outlined in the report, Roehrkasse said.
An estimated 350,000 people could be exposed to an anthrax attack by terrorists spraying the biological weapon from a truck driving through five cities over two weeks, according to the report. An estimated 13,200 people could die.
The report also includes scenarios of natural disasters to hit major cities, including a 7.2 magnitude earthquake and a Category 5 hurricane.