Alma E.M. Davidson, 71, a retired Montgomery County school teacher and department head, died Wednesday at Holy Cross Hospital.

At her retirement at Montgomery Blair High School, a position she had held for 23 years. She had been faculty adviser to the school's year book, which had won many awards.

Born in Chevy Chase, Mrs. Davidson held bachelor's and master's degrees and a doctor's equivalency degree from the University of Maryland.

She had taught at Eastern High School in Washington and at Solomons Island, Md., as well as in Montgomery County.

Mrs. Davidson was a member of the Montgomery County Teachers Association and the National Association of Retired Teachers.

She was a past matron of the Brookland (D.C.) Chapter of the Eastern Star and a member of the Past Grand Officers Society of the D.C. Eastern Star.

Mrs. Davidson belonged to the Potomac Rose Society, the Potomac Chrysanthemum Society and the National Capital Day Lily Society.

She lived in Rock Creek Hills Md.

She is survived by a son, Robert L. Marshall, of Silver Spring; a sister, Evelyn E. Mills, of Chevy Chase; a brother, Robert W. Essex, of Lanham and two grandchildren.