European Community foreign ministers wrapped up a food-aid package for Poland at prices below world levels, diplomatic sources said. The ministers agreed on the package along the lines of a proposal made by the EC's executive commission last week which Poland had accepted. The proposals provided for 200,000 metric tons of cereals, 50,000 tons of meat, and 30,000 tons of butter, as well as olive oil, rapeseed, whole milk powder, and rice. The food will be sold mostly at 15 percent below world prices, except for sugar, the sources said. They estimated that the total package would cost the Polish government from $280 million to $350 million, depending on world price fluctuations. Poland is expected to seek credit from EC countries to pay for the food, which is intended to plug supply gaps and ensure stability after months of labor unrest.