Margaret MacGregor, 78, who had helped establish the Montgomery County Commission on Aging, died May 29 at her home in Washington Grove, Md., after a heart attack.

She was the volunteer executive secretary of the commission from 1967 to 1970 and was chairman of its health Committee at the time of her death.

Miss MacGregor also helped organize the Retired Senior Volunteer Program of Montgomery County and was a member of its advisory council at the time of her death.

She was born in Ogdensburg, N.Y., and graduated from Elmira College in New York. She earned a master's degree from Columbia University.

Miss MacGregor had engaged in social and community work in New York and West Virginia. She also had served with the American Red Cross in the Far East and in Puerto Rico.

She had been with the Montgomery County Health Department in the late 1940s and early 1950s, and then was with the New York City Child Care Agency.

She returned to this area in 1961. One of her last interests involved a senior apartment complex in conjunction with her church, the Cedar Lane Unitarian Church in Kensington.

She is survived by two sisters, Grace Flower, of Emmaus, Pa., and Mrs. Harwood Taylor, of Elmira, N.Y., and a brother, Wallace R. MacGregor, of Satellite Beach, Fla. CAPTION: Picture, MARGARET MacGREGOR