BEFORE YOU SIT down to your turkey and trimmings today, we'd like to say a few words to you about kids, schools and the difficult task of feeding one by way of the other. After all, this is a holiday associated with the groaning board, and not a bad time to remember that there are many children in the country who depend heavily on the school cafeteria to give them the nourishment that they need.

How does a government agency in a large, rather decentralized country try to deal with the needs and likings of different children living in different sorts of communities, while fighting off or compromising with the demands of various lobbies that certain foods be put into--or kept out of--the children's diets? And how does it do all of this with a much- reduced budget at a time when the people most needing help are poorer than ever? To understand how these pressures are playing out in the present school lunch controversy, you should know some recent history.

Last summer Congress, at the behest of the administration, cut a billion dollars from the school lunch program--about a quarter of its budget. Part of the loss could be made up by charging more to students who aren't poor, but Congress told the Agriculture Department to come up with other cost- saving measures. Two main ideas emerged. One-- reducing the required size of meal portions--was a serious cause for concern. The other--giving schools a little more flexibility in planning meals--was not a serious threat, but it got most of the public attention.

Here we reach the Great Ketchup and Tofu Affair. The morass of regulations that already was governing school meal preparation involves such winsome concepts as "recognizable entrees," "offer- vs.-serve" and "crediting requirements" (including the hot issue of whether concentrates, such as tomato paste, should be credited on the basis of actual volume or on a "single-strength reconstituted basis"). And this suggests point one: any move in the direction of simplicity is probably a good idea.

Where the department got into trouble was in entertaining the request of school districts with Oriental pupils that soybean curd--tofu--be counted as part of the protein requirement. Tofu has lots of protein, but it sounds funny to most people. Point two: leave something out of the diet and you're guilty of ethnic insensitivity; put it in and you'll get egg foo yong on your face. Another idea was letting yogurt be counted. But this got the dairy lobby mad because yogurt can be made from dried milk-- which the government has by the mountain among its surplus stocks--while fresh dairy products must be bought from farmers.

The notion of substituting ketchup for vegetables never appeared in the proposals at all. It was a horrible possibility conjured up by nutrition advocacy groups as something that state agencies might do under color of a new authority to increase menu variety. Point three: there's a lobby guarding every dish.

The ketchup and tofu hoopla caused the administration a good deal of embarrassment before the proposals were withdrawn. This is where the Bob Cratchit of this holiday comes in. The controversy probably cost the job of the department's Food and Nutrition Service Director, G. William Hoagland-- a widely regarded analyst who also drew fire from the White House last week for the seemingly unremarkable admission that a new set of regulations was being reviewed at the highest levels.

The new rules aren't out yet, but when they emerge, you can be sure that the same sets of interests will be lined up to pick over them. When this happens, remember: it was already tough to serve a decent meal with the dollars that schools had last year. With the much smaller purchasing power that budget cuts and inflation have given schools this year, many schools--including almost 3 million children--have been forced out of the program altogether. The choice between more flexibility for schools and the present rigorous guidelines is, in a real sense, a choice between a reasonably adequate lunch and no lunch at all. That's a choice worth reflecting on a moment as you sit down to your Thanksgiving dinner.