Mary Cooke Buckner, 86, a fourth-generation Washingtonian and a public school teacher here for 46 years, died Sunday at D.C. General Hospital.

She was the senior descendent of the Jackson-Cooke family, and with other rescendants had searched family papers to trace their roots to Eliza, a slave who bartered freedom for herself and her unborn child in the early 1800s.

"Mary Ann, my grandmother, used to tell me the story of how Eliza, her mother, made sure that her baby was born free. I listened to every word as she told the story over and over again. And now I guess that I do the same," Mrs. Buckner once said.

At that time, she was preparing to bring her family together in 1976 to celebrate a memorial mass on the anniversary of the birth of her grandmother, Mary Ann Jackson Cooke, who died in 1926 at the age of 99. Mrs. Buckner was the surviving member of the fourth generation of that family in Washington.

She was the youngest of eight children of Francis Randolph Cooke, Mary Ann's son who had operated a stall at the old Center Market, now the site of the National Archives. She was the first of her family to go to college.

After graduating from the old Miner Normal School in 1911, Mrs. Buckner became a kindergarten teacher at Garfield Elementary School. She later taught second and third grades at many other elementary schools, including Slater-Langdon and Grimke, where she retired in 1957.

In 1918, she married William K. Bucker, a teacher here who went on to become principal of Armstrong High School. He retired in 1957. They celebrated their 60th wedding anniversary in July.

Mrs. Buckner had been active for many years in educational, community and church organizations. She had been a leader in the D.C. Parent-Teacher Association and had served on the board of directors of the Washington chapter of the International Association for Childhood Education.

She had been a member of the board of directors of the Old Teachers Union No. 6, and belonged to the present Washington Teachers Union.

She belonged to the Pleasant Plains Civic Association and was a former vice president of the Federation of Civil Associations here. She had served on the D.C. Public Health Advisory Board for a number of years.

As Mary E. Cooke, Mrs. Buckner had actively supported the Niagara Movement in 1909, which led to the establishment of teh KAACP.

Long a member of Sts. Paul and Augustine Catholic Church, she helped organize its Federal Credit Union and served on its board. At the time of her death she was president of the Catholic Interracial Council, of which she had been a member since it inception.

Mrs. Buckner belonged to the Senior Citizens Club of All Souls Unitarian Church. She was a member of the Venice Beach Citizens Association of Anne Arandel County, and a resident of Highland Beach, Md.

In addition to her husband, of the hosne in Washington, she is survived by a daughter, Rita B. Slie, of Washington, and five grandchildren.