Pennwalt Buyout Threatened: The Federal Trade Commission, raising antitrust concerns, threatened to block the proposed $1.05-billion takeover of Pennwalt Corp. by Paris-based Societe Nationale Elf-Aquitaine. The FTC said it had "reason to believe that the acquisition could substantially reduce competition and the production and sale" of two key chemicals. The FTC's concern centers on polyvinylidene fluoride, which is used in electrical wire insulation. A second, similar product, vinylidene fluoride, also is a target of concern. Despite the government move, analysts said they still expected the takeover to go through, although probably in a modified form.