The exact amount will be announced at a summit of world leaders and aid organizations in London on Wednesday, but in an interview with Reuters, Melinda Gates said the commitment would be "on a par" with the foundation's other big programs, like that against malaria, AIDS and tuberculosis.

In January, the foundation pledged a further $750 million for that fight on top of $650 million contributed since the fund was set up 10 years ago.

The aim of the London Summit on Family Planning is to raise $4 billion to expand access to contraception for 120 million women in the developing world by 2020.

According to United Nations figures, about 220 million women in the developing world who do not want to get pregnant, cannot get reliable access to contraception.

"Because we didn't have contraception or family planning on the agenda we weren't putting new money into it," says Gates. "We weren't saying this is a priority. So this is our moment in time to say this is a priority and we need to fund it."

Money is not the only barrier. Controlling population growth has fallen off the development agenda, rendered controversial for decades by coercive programs like forced sterilization in India in the 1970s and China's one-child policy.

It still provokes controversy, not least in the United States where Gates has been criticized by Catholic groups which tend to see contraception and abortion as part of the same issue.

"It's far less controversial than people make it," says Gates, citing a Gallup poll three months ago in the United |States. "Top of the poll was: 90 percent of Americans think contraceptives are morally acceptable. 82 percent of Catholics think contraceptives are morally acceptable. To me that's not controversial.

"It's when you start to broaden the agenda that you find the controversy," she adds.

CULTURAL HURDLES

But there are major cultural barriers in some developing countries to limiting family size.

Goodluck Jonathan, president of Africa's most populous country Nigeria, has backed greater use of birth control to head off a population boom that the United Nations forecasts will see the nation grow to 400 million people by 2050 from 160 million.

But he acknowledges the scale of the challenge. At the end of June he was quoted by the BBC as saying: "Both Christians and Muslims, and even traditionalist and other religions, believe that children are God's gifts to man".

The Nigerian government is backing an information campaign on birth control and has not ruled out legislation.

But Gates and development agencies agree that making contraception available on a voluntary basis is crucial, and will be enough to bring major economic, health and environmental benefits.

This week, the medical journal The Lancet published a series of studies that underpin the campaign.

One said that satisfying the unmet demand for contraception among women who want to limit or space their pregnancies could reduce maternal deaths by 30 percent, saving about 104,000 lives a year caused by complications linked to pregnancy and childbirth.

Better access to contraception would cut unsafe abortions, estimated to account for 13 percent of maternal deaths in the developing world. First pregnancies for very young women and those that are spaced too closely also carry a heightened risk, the study said.

An environmental study estimated that, if the UN's highest predictions of population growth prove correct, there will be a 60 percent rise in carbon dioxide emissions from energy use.

An economic analysis in the same series, based on research in Bangladesh and Ghana, found that making contraception widely available increased female participation in the work force, lifted women's earnings and enhanced overall economic growth.

DOSE OF REALISM

The majority of the funding for the campaign will not come from the Gates Foundation, but Melinda Gates believes the countries in greatest need of better family planning have both the means and the political will.

"There are at least six African countries today that are having large economic growth... Even a place like Ethiopia, it's growing so, as its economy grows, it can start to put more money into health."

The foundation can be a "catalytic wedge", taking some risk out of the equation and bringing some innovation, she says. "The causes we have picked around the world are so enormous that they take governments to come in and really fund them at large scale."

But why, given the Gates' reputation for setting ambitious targets for the eradication of some of the world's biggest health threats, is the target not to meet the unmet contraceptive needs of the whole 220 million women?

"I think it's really important, particularly in global health, to have ambitious goals but also realistic goals," says Gates. "Even meeting 120 million is going to be tough for us."

(Created by Chris Wickham, editing by Tim Pearce)

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