SUPPOSE THAT you were fortunate enough to have an income far above the average. Suppose that you got a form letter last week from C. T. Conover, the federal comptroller of the currency, asking you to take part in a survey of the ways people with high incomes handle their money. Where did Mr. Conover get your name? From your income tax return.

Mr. Conover's purpose is unexceptionable. He is not trying to sell you insurance or municipal bonds. He works for the Treasury Department, and his job is regulating banks. With other federal agencies, he has asked the University of Michigan Survey Research Center--a highly reputable organization--to carry out a study of consumers' saving and borrowing practices. But a random sample of the population won't turn up enough people with high incomes to shed much light on their habits. They are presumably the most sophisticated of investors. How are they using the new financial mechanisms? How do they prepare for retirement? Do they find the recent consumer protections useful? The financial system is changing rapidly and "as your representatives in the financial community" Mr. Conover and his colleagues want the survey to judge their own effectiveness.

The Internal Revenue Service has not given him any numbers from your return. It has given him only your name and address on a list of some 7,000 people with "relatively high" incomes. You are not under any pressure to respond. But if you are willing to take part in a confidential interview, just sign and return the enclosed card, etc.

Is it legal for Treasury to use the tax returns that way? Apparently. The IRS cites a section of the code authorizing it to provide them to Treasury officials for purposes of analysis and so forth. But internal statistical studies are one thing and this kind of extramural use is quite another.

Very few people will be reassured to know that their tax returns are being culled for special characteristics that attract the interest of various federal agencies. A return contains information of such intensely private character--and of such enormous commercial value-- that it needs to be guarded with extreme caution.

There is always a tension between the government's hunger for data and the citizen's right to privacy. In this case, the Treasury would have done better to veto the list-making and settled the question in favor of the right of privacy.