Anne (Nancy) Blaine Harrison, 58, a founder and leader of a citizen watchdog organization for the city's school system and a well known philanthropist, died Thursday of cancer at Washington Hospital Center.

A descendant of two prominent American families, she worked unceasingly to help those less fortunate than herself - especially children in the city.In 1964, she helped found the District of Columbia Citizens for Better Public Education, and worked with that organization to improve public education in the city.

"She was absolutely committed to getting things done for people," said D.C. City Council member Polly Shackleton, a longtime friend. "She was a great human being - certainly one of the most important people in this city in the field of education."

"She had a tremendous sensitivity to the needs of people less fortunate than herself even though she was born wealthy," said Flaxie Pinkett, another friend and cofounder of Citizens for Better Public Education.

"She was a person we were blessed to have in this community. She was very liberal with her money and herself . . . She is a great loss to our community," Ms. Pinkett added.

Born in Chicago, Mrs. Harrison was a great-granddaughter of Cyrus McCormick, inventor of the McCormick reapers, nad James G. Blaine, former U.S. senator from Maine, twice Secretary of State and unsuccessful Republican nominee for President in 1884.

A graduate of Vassar College, she worked for several labor organizations during the 1940s, then came to Washington after her marriage to Gilbert A. Harrison in October , 1951. Harrison was the owner and editor-in-chief of New Republic magazine for 20 years.

In 1954, her grandmother, Anita McCormick Blaine, that matriach of the McCormick family, left her $11 million of a $35 million estate.

Mrs. Blaine also left funds to create and finance the New World Foundation. Six years ago, Mrs. Harrison, as president and chairwoman of the foundation's board of directors, obtained funding for a "street law" program she wanted taught in D.C. high schools.

The program, in which law students teach rudimentary law to high school students, was started at two D.C. high schools and has spread to other high schools here and been copied in 10 states.

Jason Newman, a Georgetown University law professor organized the law program and Mrs. Harrison, playing her usual behind-the-scenes tole, told him to ask the New Yorld Foundation for the funding.

When Newman started raising objections that she might not be able to sway the board to approve the money, although she was its head, she told him, "it's my grandmother's money." He raised no further arguments, a friend said yesterday in recounting the story.

She succeeded Pinkett as president of Citizens for Better Public Education in 1967, and served in that post until 1970. Then she became executive director; the position she held until her resignation in December. The board of directors voted her the honorary title of president of the organization only last Tuesday.

She is survived by her husband and their four children, David Blaine, James Louis, Joel McCormick and Eleanor, all of the home, and a half-sister, Audrey Bird, of Winnettka, Ill.

The family suggests that expressions of sympathy by in the form of contributions to Citizens for Better Public Education, 95 M St. S.W.