Benjamin Blanken, 81, a retired general manager of Charles Schwartz & Son, jewelers in the Washington area, died Monday at Sibley Memorial Hospital after a stroke and a heart attack.

Mr. Blanken, who was born in London, came to the United States in 1905 and settled in Washington. He graduated from the old Business High School and earned a degree in accounting at Southeastern University. He also attended George Washington University.

He began working for the Schwartz firm in 1923. He was its general manager when he retired in 1970. In the course of his career, he became a registered gemologist and a specialist in diamonds.

Mr. Blanken was a member of the board of the Retail Credit Bureau in Washington and a member of the Gemological Society. He also was a member of B'nai B'rith and of the board of B'nai Israel Synagogue, formerly in Washington and now in Rockville.

Survivors include his wife, Faye, of Washington; two daughters, Joan Roth of Bethesda and Diane Mesirow of Sumner, Md.; one son, William of Potomac; one brother, Samuel R., of Washington; one sister, Gertrude Stutz of Cleveland, Ohio, and eight grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the National Jewish Hospital, Denver, or to the Metropolitan Heart Guild, Washington, D.C.