No surprises for Johnny on this one: public school lunches get a C for quantity, but an F for nutritional content in a new report card by the General Accounting Office.

As the Reagan administration moves to cut the size and quality of school lunches, the new GAO review has found that meals now served in selected high schools flunk the basic nutritional tests.

GAO said that none of the lunch formats it studied at schools in seven states met the goal of providing one third of a student's recommended dietary allowance (RDA). Some of the lunches did not even provide one fourth of the RDA, the GAO found, although most met the quantity requirements.

The congressional auditing agency recommended that Secretary of Agriculture John R. Block take a new look at the department's lunch standards and either assure that present nutrition goals are met or set "more achievable" standards.

GAO's findings parallel a study in 1977 that found school lunches generally not meeting the Department of Agriculture's nutritional requirements. USDA agreed with the findings and last year moved to establish a monitoring system.

The new GAO study was released last week, just days after the Department of Agriculture, responding to federal budget pressures, took the latter course. It proposed new regulations that redefine child nutrition standards, permitting substitute foods and smaller portions.

GAO auditors looked at conventional, fast-food and salad-bar lunch formats at high schools in Nevada, Florida, Georgia, Wisconsin, New York, California and Ohio. The conventional format, GAO said, came closer to meeting nutritional requirements than the others.

But even at that, all formats examined by GAO had "problems" in meeting the recommended levels of seven of the 14 nutrients included in the analysis. The study said that because students usually eat elsewhere at other times of the day, their luncheon menus may not harm their health.

In its response to GAO criticisms, Agriculture officials agreed the nutritional goal should be reexamined but they said that a departmental task force of food-service experts was doing just that.

The task force's conclusions, however, were discarded by the department as it prepared the new school lunch proposals. The task force said the proposals would "compromise" the nutritional integrity of the $3.5 billion program and that cost-saving measures, other than changing meal content, should be adopted. The task force findings and comments were not mentioned by USDA in its lengthy explanation of its proposals, published earlier this month in the Federal Register.

The change in lunch regulations was prompted by Congress, which instructed USDA to seek cost savings in the program without compromising nutritional integrity of the lunches and breakfasts served to more than 27 million children.

Departmental officials insisted that the three-month time requirement placed on them by Congress left no alternative but to seek savings by cutting the size of portions--in some cases by as much as 50 percent--and permitting substitutes for certain basic foods.

Under the proposals, for example, nuts and seeds and bean curd (tofu) could replace meat; cakes, cookies, doughnuts, pies, corn chips and pretzels could replace bread; pickle relish and ketchup could be counted as vegetables. Cottage cheese or yogurt could be offered instead of meat.

The proposed regulations have drawn strong opposition from consumer, nutrition and some farm commodity organizations.