TO know Theresa is to understand the power of an idea - and the women advancing it - that has shaped and energized the huge United Nations population conference now meeting in Cairo.
At age 20, the shy, pretty Nigerian seemed destined for the life of poverty and perpetual child-bearing that is the lot of most rural African women.
At 30, her lot changed. She and nine other women were given a loan, seeds, tools, and good advice by a nongovernmental organization (NGO), which they parlayed into abundant harvests. She now has more confidence, an income, and the respect of her village. What she has fewer of is children. Freed from dependence on children for status and old-age security, her family numbers only four, less than half the village average. ''I have a different view now about children,'' she says succinctly through an interpret er.
Behind the vocal debate over abortion and other controversial, reproductive-rights issues, a thousand stories like Theresa's have been told this week in the great hall where women's groups, along with other NGOs, have gathered to swap experiences, share lessons, and oversee the official conference taking place at a convention hall nearby.
Nearly all make the same point, which women's groups have successfully harnessed to mold the Cairo agenda: Women's productive and reproductive roles are inextricably linked.
''We can't say any longer that population is about those people who do family planning, while I'm over here doing agriculture, or education, or women's micro-enterprises that have nothing to do with the real story in Cairo, and it's an incredible breakthrough,'' says Joan Dunlop, president of the New York-based International Women's Health Coalition.
''Compared to 1974 and 1984, there's no question that women's groups have been able to articulate their views more clearly and more strongly to the governments involved here,'' says Joseph Chamie the deputy director-general of the Cairo conference, which is known formally as the International Conference on Population and Development (ICPD).
UN population conferences held in 1974 in Bucharest and in 1984 in Mexico City mainly stressed the need for more contraceptives and better family planning to stablilize population growth. But pressure brought by women's activists, many of whom played an influential role in planning meetings leading up to Cairo, has helped change the whole focus of global efforts to curb global population growth.
Women's groups were highly instrumental in getting the ''D'' in the ICPD - that is, in emphasizing the importance of social and economic development as preconditions to reducing population growth. But they have added a new twist to an old idea by insisting that the key to development lies in unleashing the productive potential of women like Theresa.
Unless women are given economic opportunities, credit, legal rights, and greater access to education - one effect of which is to delay marriage and childbirth - it will be impossible to slow runaway population growth, women's groups say.
IN one sense, these groups have been a victim of their own success in Cairo. Their deter-mination to guarantee full reproductive rights for women has led to a controversy with conser-vative religious groups that has dominated the official discussions and press coverage.
''This document for the first time establishes an individual reproductive right, and that's what has put the Vatican and Muslim fundamentalists into such a frenzy,'' says a long-time population activist in Cairo, referring to the 113-page draft program of action that will be debated and ratified before the conference adjourns next Tuesday.
Disagreement over the draft 20-year plan has focused sharply on abortion. The Vatican has opposed several references it said could be interpreted as condoning the procedure. At least eight countries sided with the Vatican yesterday in rejecting a compromise proposed by the European Union that would replace a call to decriminalize abortion with wording from the 1984 conference that abortion should never ''be promoted as a method of family planning.'' The plan does not require approval from all participants,
but the UN is striving for the widest possible consensus.
One reason women's groups have been so influential is that most population experts are now receptive to their basic argument - that stabilizing global population growth requires addressing problems that create the demand for large families, such as pov-erty. Another is the unity they brought to Cairo. Once a collection of disconnected NGOs, wo-men's groups have coalesced into a powerful worldwide movement.
As one leading population expert in Cairo - a woman - notes, the reputation many feminists have for being confrontational has meant the message of empowerment has not always gone down easily. But what some activists have lacked in finesse, they have more than made up in sheer political savvy.
In the run-up to Cairo, women's groups lobbied their cause with consummate skill. ''We know what's in that document - every word of it,'' says the expert, requesting anonymity.
Stabilizing world population growth ''is not simply a women's issue,'' Mr. Chamie says. ''Men and women are working together to assist disadvantaged women in many countries. We're talking about development for everyone; not simply for one group.''