About 8 million American children start school hungre everyday because only one in five U.S. schools has set up breakfast programs authorized by Congress 12 years ago, a new report by the Children's Foundation asserts.

The school breakfast program is the "most underused . . . and most strongly resisted "by local officials of any federal food program, the study says.

Foundation researchers found that only about 2 million of the 10.9 million children who eat free or low-cost school lunches also get free or subsidized breakfasts, under the Department of Agriculture programs.

The Children's Foundation, an advocacy group for nutrition programs, undertook the study as part of an effort to make the breakfast program mandatory.

The Agriculture Department agrees. "We would like to see the program expanded to children in need," department spokesman Orval Kerchner said. "We proposed legislation that would have mandated the program in the last session of Congress, but it was not enacted."

Kerchner, an administrator in the agency's Food and Nutrition Service, noted that Congress did make improvements in the overall child nutrition legislation this year, mainly raising the funding levels with amendments that President Carter signed earlier this month.

The breakfast program started as a two-year experiment in 1963, aimed at children in poor areas and those bused long distances to school. Congress made it permanent in 1975. The Agriculture Department pays state school systems from 12 to 42 cents for each meal it serves, and children pay from nothing to 25 cents per meal, depending on family income.

Many schools do not have breakfast programs because of difficulties such as schedule adjustments, the cost of hiring extra food service workers, the need for teachers to supervise the meal, and lack of facilities. The report's authors analyzed and discounted most such barriers as not "insurmountable."

They discovered, however, other obstructions. They found that many administrators feel the program is not the school's responsibility, or that it will interfere with family structure by encouraging more women to work.

Other administrators said they thought the program was "communistic" or represented too much government interference. One Souch Carolina official told interviewers that he would "rather go to hell than run a breakfast program."

Food program advocates urged Congress, before it adjourned last month, to make the program mandatory in all schools with more than 125 pupils or with large low-income enrollments. The effort failed, but the program was expanded.

Besides making the program mandatory, the foundation's report recommends more promotion activity for the program ny the Agriculture Department and state governments and "reassessment" by local officials who have resisted it.

"This administration has taken a strong stand on encouraging states to implement the program where it is needed," Kerchner said. He said the department is urging states to puch local school authorities to implement the program, using media announcments and otherwise "giving as much encouragement as we can."