WHILE AT first glance it might be construed as some arcane Supreme Court case," offer vs. serve" is actually the latest in school food-service politics -- the administration's recovery from the "tofu and ketchup" debacle.

Assistant Secretary of Agriculture Mary Jarratt, speaking before about 350 members of the American School Food Service Association meeting last week, said that this latest federal school-lunch proposal should help reduce school food costs 4 to 5 cents per plate by reducing plate waste.

In order to be reimbursed for food under the traditional system, lunchroom managers were compelled to serve each student participant a full portion of five meal items (meat, milk, bread and two portions of fruit and/or vegetables).

A few years ago, all high schools were required to begin the "offer vs. serve" menu option. "Offer vs. serve" allows a student to refuse up to two of the five meal components. If a hot dog on a bun is offered with cottage cheese, broccoli and a peach half, the student may turn down the cottage cheese and broccoli. The student still pays full price, and the school still will get reimbursed for serving the proper meal.

Food-service directors claim that it's easy to judge which foods will and will not be popular, and to save money they can decrease their orders for the less-popular food. Thus they spend less.

While high schools were required to begin the program in 1975, the plan has been optional for middle and junior high schools. President Reagan's Reconciliation Act last autumn extended the option to elementary schools. The new proposal would make "offer vs. serve" mandatory in all schools.

Parents worry about their very young children getting proper nutrition, said Shirley Watkins, director of the Memphis, Tenn., school food-service program. Giving the young ones an option to refuse certain portions of a balanced school lunch was not a subject getting rousing parental support. "Obviously," said one Takoma Park parent, "the kid will always leave the broccoli and take the Jello."

Joyce Blue, administrative aide at Petworth Elementary School and mother of a second-grader, voiced some reservations about children making their own decisions in lunch choices. "Children are children. If it was up to them they would have junk food constantly. If it was left up to the kids, they wouldn't get any vegetables at all."

In Memphis "offer vs. serve" was combined with a creative marketing program that involved parents, students, teachers and food-service workers, with the hired help of a local advertising agency. Watkins said meal participation increased 3,500 students per day and resulted in "empty garbage cans." The plan worked.

An empty garbage can is a thrilling sight for a food-service director. Apparently it's not common; an awful lot of kids throw away an awful lot of food. While the new proposal does not specifically require nutrition education, food-service managers agreed that it should be a part of any new cafeteria program.

Education is imperative to the success of the "offer vs. serve" program, according to Geoffrey Becker of the Community Nutrition Institute. "The problem isn't 'Are you going to force a kid to eat broccoli,' " but how to teach the child to prefer broccoli.

The success stories coincide with nutrition-education efforts. And food-service directors, from Corpus Christi (where meals are produced in a central kitchen and delivered to the meal sites) to New York City (where some meals are served family-style), laud the program's ability to reduce waste. A student isn't forced to take, and thus doesn't throw away, what he doesn't expect to eat.

Food-service managers find that the program not only reduces plate waste, but increases participation. More students (an estimated 3 percent) have begun buying school lunches since the program began in elementary schools. A Department of Agriculture survey, concluded last month, shows most of the students (95 percent), most of the parents (90 percent) and most of the food-service workers (80 percent) thought the program was "good."

Students enjoy making the choice, said the food-service directors. "If children are allowed to select what they want to eat, they are more likely to eat it," said Watkins of Memphis. "Our children are happy and we don't have any food wasted."

But parents wonder if their children eat properly. Elizabeth Cagan, who administrates the New York City food-service program, requires the students in her 1,200 meal sites to take "tasting portions" of the food that's offered. If a student chooses the hot dog, bun and peach half, he must take at least a bite of the cottage cheese and broccoli. If he finds he likes it, he can return to the line for a full portion.

Advocates at the Food Research and Action Center (FRAC), who fought so vehemently against the proposed meal-pattern changes (smaller portion sizes) last fall, gave at least reserved approval of the new regulations.

"It's a victory for all of us who were worried about portion sizes last fall," said Lynn Parker, nutritionist at FRAC. She adds, however, that the new policy requires the present "Type-A" meal pattern and a strict auditing system.

Presently, the "Type-A" school lunch must meet minimum requirements (adjusted for the age of the child) of five food items. Each group of food has specifications--for instance, only half of the total requirement for fruit and vegetables may be met with full-strength juice.

Parker said that the success of the program depends on the USDA maintaining the strictness of the regulations, thus retaining the integrity of the Type-A lunch. Some food-service directors at last week's meeting withheld support for the program until they were sure, for example, that potato chips could not be considered a potato, i.e. a vegetable offering.

Pat Kearney, Jarratt's confidential assistant, insisted that the USDA plans no changes in meal pattern concerning portion sizes, and said, "Here again it behooves the food-service director to serve well-balanced, nutritious meals."

Kearney said the school food-service programs would be monitored in the traditional fashion--the program gets full credit for federal reimbursement if each student has at least three full portions of food on his plate. States will have the option of tailoring the "offer vs. serve" program to their own desires. Some may require that a student take four of the five portions; some, like New York, may require that a student at least try the food he doesn't want.

The consensus, with only moderate reservation--those directors waiting "to read the fine print" of the new proposal--seems to be approval of the new approach. While many nutrition advocates express some concern about young children not getting enough fruits, vegetables or milk, they say that this plan is the best compromise. School-food services have to save money; nutrition advocates and lawmakers would like to reduce plate waste rather than portion sizes.

Anyone who wishes to express an opinion should write Stanley C. Garnett, School Programs Division, Food and Nutrition Service, USDA, Alexandria, Va. 22302.