The Soviet Union has bought 250,000 metric tons of corn, its first large purchase since a U.S.-Soviet grain agreement expired Oct. 1. Officials said talks to negotiate a new agreement are scheduled for this week in London . . . Akron, Ohio-based B. F. Goodrich Co. said it is negotiating the sale of its aircraft tire operations to Michelin Tire Corp., headquartered in Greenville, S.C. . . . Tropicana Products Inc. announced that it has voluntarily dismissed its suit against Richard A. Hamilton, a former engineer for Bradenton, Fla.-based Tropicana . . . Houston-based Baker Hughes Inc. reported that the number of working oil and gas rigs totaled 914 this week, down four from the week before. A year ago, the count totaled 1,104.