The Washington Post - while coming out four-square for schoolchildren eating lunch - disapproves of proposed Department of Agriculture regulations to encourage them to do so.

On July 7, The Post expressed its editorial disapproval ["No Candy in the Morning"] of USDA's proposal to regulate the sale of certain foods that compete with federally funded school lunches. I believe your editorial misses the mark in several respects.

First, it seems your quarrel should be less with the Department of Agriculture than with Congress, which in 1977 specifically authorized the department to take action on competitive foods. The Post obviously believes Congress should have left this authority with school districts. Members of Congress obviously believe that it is a federal responsibility to protect the integrity of child nutrition programs, for which federal taxpayers spend $3 billion a year.

Today, more than in the past, there is a concern that federal funds be used efficiently and effectively to carry out the purpose for which they are intended. That's why conditions are attached to grants of federal funds. No school district is reimbursed for meals served to students unless those meals meet certain minimum nutritional standards set by the USDA. Surely, The Post would not suggest that it is inappropriate for the USDA to set such standards.

But The Post seems to believe that setting nutritional standards on foods that compete with school lunches is a frivolous action. It is not. Various studies indicate that:

Sugar contributes to dental caries, and dental caries are a major problem among young people;

Iron intake is low for a significant portion of children in the 6 through 17 age group;

Many children in the United States consume less than the recommended dietary allowances for some vitamins, such as A and C;

Snacks contribute more total calories to children's diets than any other single factor, but contribute less to nurtrient levels than meals do;

Snack calories come mainly from fat and sugar.

In light of these facts, the congressional action does not seem inappropriate of frivolous. One supporter, Sen. Robert Dole (R-Kan.), said in 1977 that "there is a need to reassess the priorities and take a close look at preventive health measures which can be taken in the child feeding programs. I am suggesting we do have a need to at least try to make our children understand the necessity for eating balanced, nutritious meals."

Former representative Albert Quie said the amendment provides for "a limited power to be used sparingly to encourage the sound nutrition and nutritional habits of school children." Dole and Quie are generally regarded not as federal interventionists but as advocates of limited and efficient government.

Second, your editorial suggests that the federal government is instructing the principals of 90,000 schools to lock up the vending machines every morning. We do no such thing. We hope the machines will remain open - stocked with foods such as fruits, fruit juices, vegetables and nuts. The same is true for school snack counters.

Finally, your editorial seems to suggest that local school officials and school boards oppose federal standards. That hardly seems to be the case. Eighty-seven percent of school personnel who have commented on our earlier proposal either supported or wanted a stricter regulation.

I agree with the Senate Committee on Agriculture, which stated that the competitive-foods amendment was formulated because, "It is counterproductive for the federal government to attempt to provide nutritious, health-supporting meals through child nutrition programs and at the same time permit foods of low nutritional value to compete directly with nutritious meals."

I am surprised to find The Post in the opposite corner.