The Department of Agriculture's school lunch program sent ground pork contaminated with two dangerous pesticides to school systems in Louisiana and Arkansas, and children ate it.

Carol Tucker Foreman, Agriculture's assistant secretary for food and consumer services, said inspectors have recovered about 13 of the 20 tons of contaminated meat shipped to the two states. The remaining seven tons cannot be found.

"We have every reason to believe that the product in those boxes has been eaten," she said. "It's a terrible thing to have happen."

The pork may have been eaten by as many as 5,000 children in schools throughout most of Arkansas, she said. It was also sent to cafeterias in 38 Catholic schools in the New Orleans area, although inspectors had not determined by late yesterday how much of it had been served there.

Dangerously high levels of chlordane and heptachlor, termite and ant-killing pesticides, were discovered in USDA tests at the plant in Oklahoma City where the pork was packaged. The tests were conducted in late March -- about 10 days before the pork was shipped to Little Rock and New Orleans -- but the samples were not analyzed and the results reported until about six weeks later, Foreman said.

Children who ate a regular, 3-to-4-ounce portion of the meat should have experienced no problems, Foreman said. A larger portion could cause nausea and headaches, although no school systems in the states reported any such problems, he said.

The two pesticides were banned for most uses in 1975 by the Environmental Protection Agency after they were found to cause cancer in laboratory tests on mice and rats, a reliable indication of a cancer hazard to humans, officials believe.

Chlordane and heptachlor were once widely used in home gardening and in agriculture, mainly on corn grown as an animal feed. The result, EPA said, is that "virtually every person in the United States has residues . . . in his body tissues." Residues of the pesticides also have been found in unborn babies and in mother's milk.

No one can say how the frozen pork became contaminated, but presumably it was from hogs feeding on contaminated grain.

After farmers complained of severe economic hardships, EPA permitted them to gradually phase out the pesticides. Selected use on some crops will be permitted as late as July 1983. Farmers are allowed for the next two years to use heptachlor to spray small grain and corn crops when they are seeded.

Foreman said Agriculture does not know where the pork originated and no system currently exists that would show where the hogs were raised.

"We have been telling Congress and the public for two years that we do not have the scientific capability to determine whether or not every piece of meat that goes through [packing houses] is free of contamination," Foreman said.

It was almost by happenstance, she said, that USDA discovered the presence of the pesticides. The investigators at the Oklahoma packing plant were not looking for either chlordane or heptachlor but were sampling meat to determine if any had been contaminated by the cancer-causing PCBs -- polychlorinated biphenyls -- that leak from old transformers.

After the tests were made in Oklahoma in late March, samples were sent by mail to the Agriculture Department laboratory in St. Louis. They were not immediately analyzed, but set aside for several days, Foreman said, while technicians examined, on an emergency basis, pork and beef from Iowa that was thought to have been contaminated by another chemical.

Finally, on May 6, the tests on the pork were completed and the laboratory notified the Agriculture Department that in three of the six samples of pork analyzed there were unsafe levels of chlordane and heptachlor. In one sample there was 10 times as much heptachlor as is deemed acceptable.

It was not until late last week however, that the Agriculture Department began contacting school officials in Arkansas and Louisiana. Foreman said it took that much time to find where the pork had been shipped.

Most of this week inspectors have been going through school warehouses in Little Rock and New Orleans searching for the pork shipped from the Wilson Packing Co. in Oklahoma City. For the most part, they have not been telling local school officials precisely why.

"What was the trouble with it anyway?" John Schloegel, food service director for New Orleans' parochial schools asked a reporter late yesterday as inspectors went through his warehouses and schools. "I haven't heard yet."