Mary Elizabeth Power, 69, a retired teacher in the Montgomery County public school system who was active in professional and service organizations, died Tuesday at George Washington University Hospital. She had cancer.

Miss Power was born in Follansbee, where she taught in public schools for 19 years.

In 1952, she joined the Montgomery County school system and moved to Bethesda. While teaching, she earned a master's degree in education from George Washington University. She was teaching at Bethesda Elementary at the time of her retirement in 1973.

Miss Power was a former president of the Theta Chapter of Delta Kappa Gamma, a professional organization, and a former treasurer of Phi Delta Gamma, another professional organization. She was the treasurer of the Montgomery County Retired Teachers Association, a life member of the National Education Association, and assistant corresponding secretary of the Colombian Women, a George Washington University group. For five years, she served as a volunteer driver for the Meals-on-Wheels program in Montgomery County. She also was a member of St. John's Episcopal Church.

Miss Power's survivors include a sister, Esther Power, with whom she lived in Bethesda, and two brothers, Tom Power of Wheeling, W.Va., and Harold Power of Orlando, Fla.

The family suggests that expressions of sympathy be in the form of contributions to St. John's Episcopal Church, Bethesda, or to the American Cancer Society.