USX said it will post a $300-million charge.

The steel and oil conglomerate said the after-tax charge against 1986 earnings is a result of its plan to redeem $2.9-billion worth of bonds issued in connection with its 1982 acquisition of Marathon Oil Corp. The company said the redemption also would reduce its financial costs by more than $140 million per year. “The redemption . . . is a key element in the corporation’s ongoing restructuring efforts, and represents a major step in reducing current financial costs,” USX Chairman David Roderick said in a statement.