The cause was breast cancer, said her sister, Penelope West.

Ms. Dunlop devoted herself to expanding women's rights to control their own bodies. The right to say no to a request for sex was endorsed as a universal guideline by more than 180 nations at a conference in Beijing in 1995. Ms. Dunlop lobbied the delegates as president of the International Women's Health Coalition, an advocacy group that supports 50 health projects in eight countries. She held the post from 1984 to 1998.

Her leadership in women's issues grew from her involvement in organizations dedicated to controlling population. She believed that if women have better living standards and more independence, they will be empowered to decide how many children they will bear.

"When we say population policy, people think family planning, and we're saying it's far more than that," she said in 1994 in an interview with The New York Times.

That year, she summoned 15 colleagues to London in advance of a United Nations conference on population and development in Cairo. They wrote the "Women's Declaration on Population Policies," a set of guidelines that the United Nations ultimately adopted. It was the first international agreement on population policy that made women's rights a central concern.

Ms. Dunlop had an illegal abortion as a young woman in England, an experience that fueled her campaign to improve women's reproductive choices, she said. She was also angry at the rise of the anti-abortion movement in the United States, which she perceived as "an organizing tool" for conservatives promoting their broader political agenda.

"It's about getting people onto the street," she said in a 2004 oral history. "It's getting political activism for a much broader purpose."

She often directly attacked the Vatican and conservative politicians, including President Ronald Reagan, on the abortion issue.

"To give the unborn child — I don't care what stage of gestation they are — preference over the woman in whom parents, teachers, society, culture has deeply invested, and say that investment has less value than a bunch of cells, is just to me an outrage," she said in the oral history created by Smith College.

Joan Marie Banks was born in London on May 20, 1934, and grew up in a London suburb that she described as "Stockbroker Tudor." Her father was deputy chairman of British Petroleum, her mother an American. On a visit to her American relatives when she was 12, she fell in love with America. Several years later, she applied to Vassar College and was accepted, but her parents refused to let her go, fearing they would never see her in England again.

Remaining in Britain, she graduated from Queens Secretarial College in London. After working at the BBC and in other jobs, she went to the United States and became a secretary at a Manhattan advertising agency. Through family connections, she was hired by the Ford Foundation, where she worked on urban policy projects that became a blueprint for the Johnson administration's War on Poverty.

She went on to work in the New York City budget office under Mayor John V. Lindsay and the Fund for the City of New York foundation and as an adviser to John D. Rockefeller III on population issues, drawing on her Ford Foundation work. At her employment interview, she told Mr. Rockefeller about her own abortion.

"He listened with great attentiveness," she told The Times in 1998. "I sometimes wonder if that wasn't what got me the job."

The job was with the Population Council, which Mr. Rockefeller founded in 1952 to provide governments with scientific research on population questions. Ms. Dunlop helped broaden its research to include gender roles and sexuality, and she introduced Mr. Rockefeller to feminist leaders, including Germaine Greer and Gloria Steinem.

Ms. Dunlop was later vice president of public affairs for Planned Parenthood in New York and an assistant to Vartan Gregorian, president of the New York Public Library.

Ms. Dunlop's marriages to Peter Dunlop and Edward Deagle ended in divorce. She once said she was never "faintly interested" in having children. In addition to her sister, she is survived by her brother, Peter Banks.

On her last day of work at the International Women's Health Coalition in 1998, Ms. Dunlop was presented with a volume of letters from women around the world describing what she had done for them.

"It's almost better than an obituary," Ms. Dunlop said on the occasion, "because you're not dead."