Standard Oil Co. restructured its long-term debt.

The restructuring will save the Cleveland-based company as much as $30 million in interest expenses in 1987 and additional savings in later years. The actions, however, will also mean a charge against earnings of about $30 million after taxes in the fourth quarter, which ended Dec. 31, because the company had to pay a premium to retire some of its debt. Earnings for previous quarters of 1986 will be restated to reflect the effects of the debt restructuring. The charges in the first nine months of 1986 were $4 million after taxes. The firm will issue new, lower-cost debt as part of the restructuring.