The Soviet Union has bought an additional 500,000 metric tons of U.S. corn for delivery this year under a new long-term agreement that began Jan. 1, the Agriculture Department said Thursday.

It was announced Jan. 8 that Moscow has been allocated $900 million in short-term credit to buy U.S. commodities. An additional $100 million is to be allocated later.The credit package included $530 million for feed grains, primarily corn; $165 million for wheat or flour; $130 million for protein meals, mostly soybean; and $25 million for poultry meat. Also, $50 million was earmarked for transportation costs.