Roman Catholic and Muslim countries want to reduce the emphasis on family planning and increase parental authority.

Countries like Libya, Sudan and Argentina, backed by the Vatican, argue that there is a drift towards accepting abortion and towards an erosion of family and religious values.

Environmental Correspondent Robert Piggott: "Abortion is a sensitive issue"

But the majority of nations agree with decisions made five years ago in Cairo, that better sex education, birth control advice and access to contraceptives is the way to reduce population growth.

UN Secretary-General Kofi Annan said: "Too many women still cannot choose when or whether to become pregnant [and] too many women resort to abortions that are not safe."

The UK International Development Secretary, Clare Short, told the conference that keeping the truth from sexually active adolescents is not the way to reduce population growth.

UK International Development Secretary Clare Short

She said that 500,000 women die every year as a result of pregnancy, 15% of them from unsafe abortions.

"One billion adolescents all over the world are sexually active ... we can't go on keeping them ignorant," she added.

One Catholic country, the Philippines, has accepted the education argument and is providing sex education and contraception in defiance of the Church.

Funding shortfall

The UN General Assembly sessions on population is an attempt to upgrade the Cairo agreement.

David Willey from Rome says the Vatican leads the conservatives

Since 1960 the world's population has doubled to 6bn and there are fears that without action it could be as high as 10bn by 2050.

The other issue testing the meeting in New York is money. Nobody is spending as much on population polices as they promised in 1995.

The rich donor countries are only spending about a third of what they promised.

The conference, at the UN's New York headquarters, has three days to come up with a final document.