UNITED NATIONS -- The General Assembly on Wednesday began debating an action plan first drawn up five years ago to limit world population growth, although developing countries remained deeply divided over some aspects of the plan.

Most of the plan -- which seeks to freeze the world's population, now 6 billion, at 9.8 billion in 2050 by improving the status of women -- is accepted and currently being put into effect.

But a small group of conservative Muslim and Roman Catholic third-world countries, backed by the Vatican, continues to oppose certain aspects.

During negotiations Wednesday those countries, which include Libya, Egypt, Argentina, Sudan and Nicaragua, pressed on with their campaign to water down provisions calling for safe abortions, sex education in schools and contraceptive advice for young people.

In his opening address to this special session of the Assembly, Secretary-General Kofi Annan recounted some of the progress made in population control since the first world population conference held in Bucharest 25 years ago.

He said, for example, that the average family size in third-world nations had fallen from five children to less than three. And he said that today 60 percent of couples practice family planning as opposed to 30 percent then. And infant mortality rates have improved from 140 per thousand to 80.

But the world's population is still rising by 78 million every year and much more needs to be done, he said.

"We have to stabilize the population of this planet," the secretary-general said. "Quite simply, there is a limit to the pressures our global environment can stand."