U.S. Trade Representative Clayton K. Yeutter said he has been on the phone with European Community officials, who want to avert stiff new tariffs on a wide range of food items from Europe. He told the Foreign Trade Assn. of Southern California in Los Angeles that he was insisting on full compensation for $400 million worth of lost sales of U.S. grain and sorghum to Spain. "We'll know between now and Friday if we will get full compensation," he said in his address. "If we do not reach agreement, retaliatory action goes into effect one minute after midnight Thursday."