PORT-AU-PRINCE, HAITI - The difference between life and death in Haiti is now an ordinary bar of soap.

Soap could slow the terrifying cholera outbreak that is quickly spreading and has just in the past week entered the ravaged capital, according to health-care specialists and international aid groups.

But in the squalid slums of Port-au-Prince and the river towns where the cholera outbreak began three weeks ago, many Haitians held up their hands and shook their heads, saying they had no soap to stop an infection that is spread by contaminated food and water and in which vigorous hand-washing, especially after using the toilet, is the No. 1 way to save lives.

A cake of yellow Haitian soap costs about 50 cents. But many Haitians do not have soap because they cannot afford it. More than half the population lives on less than $1.25 a day.

"They buy food instead," said Gaelle Fohr, a coordinator of hygiene programs in Haiti for the U.N. Children's Fund.

"We borrow, we buy, but right now, we don't have any soap in the house, I am sorry to say," said Joceline Jeune, living with three children in a hillside shanty at the edge of a displaced-persons camp, as a gutter filled with greasy, gray water flowed inches from her front door.

When confronted by dubious toilets or fly-specked markets, people here daily use the expression "Mikwob pa touye ayisyen," which translates to "Germs don't kill Haitians."

"As hard as it is to believe, Haiti still needs soap. They have many needs, but soap - and access to clean water - is absolutely essential to fight cholera," Nigel Fisher, the top U.N. humanitarian coordinator in Haiti, said in an interview.

There are plans for more water trucks, and more chlorine in water tanks, wells and distribution points. But building a modern water and sanitation system will take years. By contrast, experts say, soap is fast and doable, allowing people to clean their hands.

Foreign governments, international aid groups and individuals have sent more than $3.4 billion in humanitarian aid here in the 10 months since a tremendous 7.0-magnitude earthquake struck the capital, killing about 300,000 people and displacing more than 1.5 million, according to the Haitian government. But poverty is so deep, needs can seem bottomless.

"Haiti has crowded slums, poor hygiene, incredible poverty - before and after the earthquake. This is an extremely contagious, extremely virulent strain. It can kill in a few hours - unless you get help. We have well over a million people in camps; we have a disease that spreads by hand, mouth, touch, water. It can lie dormant for five days. You cannot tell who is infected," Fisher said. "The country is now facing a tremendous challenge with limited resources."

Experts at the Pan American Health Organization forecast that 200,000 Haitians will show signs of the disease, while it is possible that a million will be infected but remain asymptomatic carriers still capable of spreading the potentially deadly bacteria.