According to the ISO assessment, Mr. Mirel said businesses located in D.C. were deemed 100 percent more likely to be targeted for a terrorist attack than their counterparts just across the borders in Maryland and Virginia.

ISO provides 1,500 insurers with underwriting, statistical and actuarial services as well as claims information and analyses, consulting and technical services, policy language, information about specific locations, fraud-identification tools, and data processing.

Concerning ISO terrorism projections for Washington, "These assumptions are just off-the-wall," Mr. Mirel told National Underwriter.

If implemented, he said, the price for insurance in D.C. could be two-to-three times that in Maryland and Virginia.

"Who would stay in D.C.?" Mr. Mirel asked.

Dave Dasgupta, a representative of ISO, emphasized that there is no current dispute between ISO and D.C. ISO, he noted, has not yet filed rates.

Rather, Mr. Dasgupta said, ISO has had informal discussions with regulators and is trying to understand their concerns.

It is, he said, a very complex issue.

"We don't have a lot of historical data on terrorism risk," Mr. Dasgupta said.

He added that ISO is under tremendous time pressure to develop terrorism insurance rates. Under the recently enacted Terrorism Risk Insurance Act, which creates a federal reinsurance backstop for losses caused by acts of international terrorism, insurance companies must offer terrorism coverage to all commercial policyholders by Feb. 24.

"We are trying to work as quickly as possible to make a filing," Mr. Dasgupta said.