The standard school lunch served to approximately 25 million children every school day may be detrimental to children's health, according to a recent General Accounting Office report.

The national school lunch program, which began 40 years ago as a means of using surplus farm products, cost the federal government more than $2 billion in fiscal 1977. It dictates a standard meal that provides one - third of the participant's recommended dietary allowances and is served free or at reduced cost.

The GAO report said that while the standard lunch "provides a valuable source of nourishment for some children," it may lead to obesity in others and is not effective in combating iron deficiency, prevalent among school - age children, because of large portions and a lack of supplemental nutrients such as iron.

The school lunch must meet standards prescribed by the Secretary of Agriculture. Currently those standards dictate that participating schools serve a daily consisting of the following:

One - half pint of milk.

Two ounces of meat, poultry, fish, or equivalent substitute such as cheese, beans, or peanut butter.

A three - fourths cup serving of two or more fruits or vegetables.

One slice of whole grain or enriched bread, or equivalent.

According to the analysis by GAO, Congress' auditing arm, this menu is part of the problem. The report said that the meal "is often presented in a form or content which discourages student participation..."

The Agriculture Department's Food and Nutrition Service responded to the criticism by saying, in part, that "there are no ways of addressing these concerns short of abandoning nationally established meal standards."

FNS suggested emphasizing nutrition education in schools and encouraging schools to "eliminate the sale of snack foods during the lunch period."

Making the lunches served in 81 per cent of the nation's schools more palatable and relevant to children's nutritional needs is not the only mandate of the national school lunch program. When the program began, its purpose was twofold: "... to safeguard the health and well - being of the nation's children and to encourage the domestic consumption of nutritious agricultural commodities and other food."

Local food purchases by schools participating in the NSLP account for about 1.5 per cent of the overall U.S. food market, said the report. This along with the fact that school lunch programs increase food intake "provides some basis for assuming that NSLP strengthens the demand for agricultural products," it noted. However, no study has determined the precise impact of these increases on the agricultural economy.

The GAO report urged the Secretary of Agriculture to require a "formal systematic evaluation" of the school lunch program in cooperation with the Department of Health, Education, and Welfare.

In 1975, the report said, 25.4 million students ate program - funded lunches; 9.9 million of them received free or reduced - price lunches. However, the 1978 budget analysis states that the federal government subsidizes each meal under this and other programs by 25 cents, regard less of participants' need.