White Plains, New York-headquartered Nynex Corp is still cutting costs and says it intends to cut its work force by 1,400 to 1,900 management employees in the first quarter of next year: the reduction will be accomplished under a new Force Management Plan, announced in principle in April and introduced on Monday, and will be implemented by individual Nynex companies in order to achieve their own business plans; cuts will include 325 to 425 of the managers at New England Telephone; 500 to 600 of the 9,800 at New York Telephone, and 400 to 450 of the 6,300 at Telesector Resources Group; Worldwide Services and Nynex Corporate make up the rest.