Lorimar and Telepictures shareholders will vote Feb. 6 on a proposal to merge; the effective date of the merger is expected to be Feb. 18, Lorimar said . . . Cetus Corp. and Eastman Kodak reported that they have entered into an exclusive business relationship to develop new products for "in vitro" human diagnostics . . . In a filing with the Securities and Exchange Commission, L. F. Rothschild, Unterberg Tobin Inc. reported that it holds a 5.9% stake in Citadel Holding Corp. of Pasadena . . . Lockheed Missiles & Space Co., a unit of Lockheed Corp., received a $774.5-million Navy contract for Trident II ballistic missile development and production . . . Sources said the International Monetary Fund banned new loans to Sudan, which owes the agency about $218 million in interest payments that are more than six months overdue . . . Pan American World Airways reported that it flew 2.128 billion revenue passenger miles last month, up 5.5% from January, 1985.