NIAGARA MOHAWK <NMK> TO CUT COSTS Niagara Mohawk Corp said it is "cautiously optimistic" about results improvements for 1987 and said it is studying measures to cut operating costs. These measures include freezing management salaries, abolishing vacant positions and reducing overtime. A spokesman said the company had no current plans to lay off workers. The company declined to say how much the cost savings would amount to. A five year forecast is expected to be issued in early summer, a spokesperson said. The company said it has redeemed about 273 mln dlrs in high cost debt during 1986 and hopes to redeem more debt this year. For 1986, Niagara Mohawk's earnings per share fell to 2.71 dlrs from 2.88 dlrs in 1985.. The company said earnings reduced primarily as a result of a reduction early in 1986 in earnings return on equity allowed by the N.Y. State Public Service COmmission. Niagara said it is concerned about the continued lowering of authorized return and has reinforced petitions to grant a fair return on equity.