The letter of concern about the study, which was mandated by Congress and has been underway for months, was written by staff of the American Insurance Association in Washington. Also represented on the letter were the National Association of Mutual Insurance Companies, the Property Casualty Insurers Association of America, the Reinsurance Association of America and the Surety Association of America.

The letter says both insurers and reinsurers are confused about how they should respond to some questions.

Some members of insurance and reinsurance trade groups "specifically asked some of the undersigned trade organizations to encourage Treasury to accept survey responses that included an explanatory field allowing companies to elaborate on their responses," the letter said.

The letter added that the difference in responses is likely to be compounded by the nature of the survey and that inconsistencies in survey questions that bedevil insurers are confusing reinsurers as well.

The department wants to use the answers to the questions it is posing to help it respond to a mandate from Congress to report by June 30 on the effectiveness of the program and the likely capacity of the industry to offer insurance for terrorism risk after the current program expires Dec. 30.

The report, mandated by the legislation enacted in October 2002, also asks the Treasury Department to report to Congress on the availability and affordability of such insurance for various policyholders.

The letter is being sent against the background of a hearing on the effectiveness of TRIA that will be held Thursday by the Senate Banking Committee. A number of trade group officials from both the p-c insurance industry and the real estate industry will testify, as will Robert Hunter, a former Texas and federal insurance commissioner and now director of insurance for the Consumer Federation of America.

A Treasury Dept. staff official, Brookly McLaughlin, responded to the letter by saying that the agency "appreciated the feedback" and is "reviewing" detailed comments.

Ms. McLaughlin added that, "We value the participation of industry and outside experts and incorporated many of their suggestions while developing the survey."

But, she added, "We are confident that the survey approach and methodology is sound." Ms. McLaughlin explained that the survey was designed to elicit detailed data, without being overly burdensome to participants and "we are confident that the surveys will yield important, unique and statistically valid information for the report to Congress."

Ms. McLaughlin did note that the agency "appreciates the suggestion that we use outside data sources in addition to the TRIA survey." In fact, she said, "the Treasury study will use significant amounts of information from sources other than the survey."