I was initially baffled by the editorial attacking efforts to require truth in pizza labeling {Aug. 9}. The Post is not exactly renowned for resenting government intrusion in the marketplace, so I was at first slightly bewildered to find among its editorials a free-market broadside against the real-cheese label requirement.

Upon closer examination, though, the real reasoning became clearer. The Post objects to the labeling requirement not out of fear that government will become a mere tool of the dairy industry (Big Cheese as Big Brother?), but because it's "better for the customer" to eat artificial cheese instead of real cheese on pizzas (emphasis added).

Forget for the moment that casein, the main ingredient of artificial cheese, is also an important ingredient in wallpaper paste. What's interesting here is that The Post is making the decision for all of us that artificial cheese is better than real cheese and wants to deny consumers the information they need to be able to make their own decision in the supermarket.

I like real cheese. Many of my constituents earn their livelihood from real cheese. If we enact this labeling requirement, I think consumption of real cheese will rise. But the decision for real cheese, or for the artificial casein "product," should not be made by government, or The Post, or the dairy industry. It should be made by informed consumers.

-- Robert W. Kasten Jr. The writer is a Republican senator from Wisconsin.

Yes, there is probably some truth in what you say about the pizza labeling debate. Unfortunately, what you called an ''illuminating little vignette that tells you a lot about life in Washington'' tells more about life on The Washington Post's editorial staff.

For example, the illumination is focused in only one direction -- toward the dairy lobby. Is there not also a frozen pizza lobby? If you had done your homework you would have found that they have a very energetic cadre of lawyers working for the frozen pizza makers.

You see, the whole point of this ''micro-grievance'' is not what the ''dairy lobby'' or the frozen-pizza lobby or even the government wants. The point is what the consumer should know and when he should know it. Is the information in a form he can use to decide how to act on his own behalf?

Last month a number of your competitor newspapers ran consumer surveys that indicated a vast majority of the consumers did not know that a frozen pizza was made with anything other than real cheese. If you ever tried to read the small type, printed in red ink, over tomato sauce that passes for an ingredient label you would understand why consumers don't know what is in the pizza.

But, thanks to you and the other news editors, the question is being resolved in the marketplace. If you check you will find many of the frozen pizzas now are made with cheese because that is what the consumer apparently wants. Labeling is getting better and more legible. With all these changes the price has not increased enough, if at all, to discourage sales. So you see, publicity, such as your editorial, helps to make consumers aware. The consumer is the power in the market, not the lobbyist on the Hill.

-- R. F. Anderson The writer is executive director of the National Cheese Institute, Inc.