MANILA, Philippines — Maria Susana Espinoza wanted only two children. But it was not until after the birth of her fourth child in six years that she learned any details about birth control.

“I knew it existed, but I didn’t know how it works,” said Ms. Espinoza, who lives with her husband and children in a squatter’s hut in a vast, stinking garbage dump by Manila Bay.

She and her family belong to the fastest-growing segment of the Philippine population: very poor people with large families. There are many reasons why this country is poor, including feudal patterns of land ownership and corrupt government. But there is a compelling link between family size and poverty. It increases in lock step with the number of children, as nutrition, health, education, and job prospects all decline, government statistics and studies show.

Birth and poverty rates here are among the highest in Asia. And the Philippines, where four out of five of the country’s 91 million people are Roman Catholic, also stands out in Asia for its government’s rejection of modern contraception as part of family planning.

Acceding to Catholic doctrine, the government for the past five years has supported only what it calls “natural” family planning. No national government funds can be used to buy contraceptives for the poor, although anyone who can afford them is permitted to buy them. Local governments can also buy and distribute contraceptives, but many lack the money.

Distribution of donated contraceptives in the government’s nationwide network of clinics ends this year, as does a contraception commodities program paid for by the U.S. Agency for International Development. For years it has supplied most of the condoms, pills, and intrauterine devices used by poor Filipinos.

“Family planning helps reduce poverty,” President Arroyo said in a 2003 speech that detailed her approach to birth control. But she said then and has since insisted that the government would support only family planning methods acceptable to the Catholic Church. Ms. Arroyo, 61 and a grandmother with three grown children, said in 2003 that when she was a young mother, she took birth control pills. She said that she later confessed to a priest.

At the Manila garbage dump, Ms. Espinoza said she has been lucky. A nongovernmental organization with health workers who regularly visit the dump told her that an intrauterine device could prevent her from having another baby. She plans to visit a clinic this month to get an IUD.

The organization that is helping Ms. Espinoza agreed to introduce this reporter to her on condition that it not be named. The group’s health workers said they fear retaliation and harassment from officials in the national and city government, as well as from the Catholic Church.