Mrs. Das cannot afford to die. Her husband is out of work. Her $50 a month earnings keep hunger at bay for her 11-year-old daughter, Asha, and her extended family. Before she became a prostitute, she had been making $10 a month as a maid and her family was down to one meal a day.

The Sonagachi project pays 180 prostitutes about $1 a day each to spread the word about AIDS and condoms. The British Government, long the colonial power in India, pays for the project and is one of the largest foreign aid donors supporting health programs here. This year the Indian Government, with about $50 million in financial backing from the World Bank, will begin using nonprofit groups and Government agencies in a nationwide effort to mobilize prostitutes against the disease. The project in Sonagachi costs only about $210,000 a year.

''The experience from other parts of the world and from Sonagachi suggests that such efforts are the single most important thing that can be done to try to control the epidemic,'' said Prabat Jha, an epidemiologist at the World Bank who is team leader for its AIDS project in India.

The Consensus

Taking Action, Then Expanding

One recent morning a group of prostitutes sat on the balcony of their brothel overlooking a vibrant, clogged lane in Sonagachi. It was too early for customers, so the women's faces were free of any makeup. Over the jangling of hand-pulled carriages and the cries of hawkers selling papayas, they spoke of the poverty that had driven them into the sex trade.

Milan Sarkar, a 21-year-old in a loose orange shift, was married at 15 and abandoned by her husband at 16, with an infant son, Anoop, to raise. There is no government safety net here, so a year ago she went to Sonagachi. Her income now supports her parents, two siblings and her 5-year-old son. Ms. Sarkar shields Anoop from the knowledge of how she makes a living, telling him only that she has to go to work while he stays with his grandparents.

Ms. Sarkar said she refuses to have sex without a condom, but some drunken men force themselves on her, while others tear the condoms with their nails so they will peel off during sex.

''I'm very frightened about AIDS,'' she said. ''My son and my whole family depend on me. My father is old and won't be able to continue working. I have to live here for them. And it is a terrible pressure.''