PORTLAND — A Falmouth woman who has been with UNUM Corp. for more than 20 years was named Tuesday to head the UNUM Life Insurance Co. of America, the corporation’s largest business unit.

Elaine D. Rosen, 43, will take over Jan. 1, succeeding Stephen B. Center, who also serves as executive vice president of UNUM Corp.

Center, who plans to retire in 1998 after 35 years with UNUM, will expand his responsibilities with the corporation next year, focusing on business strategy and opportunities to create greater value for customers and shareholders.