The battle against avian influenza in poorer countries will cost at least $1.5 billion over the next few years, both to suppress the disease among poultry and to prepare for the possibility it will become widespread among humans, according to estimates presented Wednesday at an international meeting.

About $500 million will be required to fight the H5N1 influenza strain in poultry, by far the best way to prevent bird flu from triggering a long-feared human pandemic, according to experts gathered at World Health Organization headquarters. Similar amounts are needed for improving the surveillance and treatment of human infections of the disease, and for stockpiling antiviral drugs and an experimental H5N1 vaccine.

The Bush administration last week proposed a $7.1 billion pandemic flu preparedness plan, including $251 million for planning in foreign countries, mostly in Southeast Asia, where the H5N1 strain has circulated for about two years. The U.S. government has already spent about $30 million on bird flu matters in that region, much of that money originally earmarked for tsunami reconstruction.

Africa, meanwhile, needs at least $170 million to increase flu surveillance, equip laboratories and train people, according to the Inter-African Bureau for Animal Resources. Experts expect that bird flu, which has spread from Southeast Asia to Eastern Europe, will be carried to Africa soon by migrating birds.

There are an estimated 1.1 billion chickens in Africa, mostly kept outdoors, where contact with wild birds is possible.

"Obviously Africa needs a lot of help. . . . We believe many lives and livelihoods would be lost with any outbreak of the avian influenza," Rachel Arunga, a delegate from Kenya, said at the conference.

Researchers said one major focus should be to limit contact between humans and poultry. Bird flu has infected at least 125 people and killed 64, and almost all of those cases involved close contact with infected birds.

In a measure to decrease human contact, a Vietnamese official said his country this week banned the raising of poultry in the downtown districts of Hanoi and Ho Chi Minh City. The sale of live birds at markets, and killing or plucking them there, were also prohibited.

The official, Bui Ba Bong, the vice minister of agriculture and rural development, said his government has recommended that farmers not raise ducks and chickens together. Unlike chickens, many ducks survive H5N1 infection and excrete the virus for prolonged periods in droppings, which can then infect other birds.

Vietnam has vaccinated 80 million birds against the virus, with a goal of 150 million. The country has reported 92 human cases, more than any other, and 42 deaths. Vietnamese scientists are developing an experimental human vaccine against H5N1.

Three international drug firms, Chiron Corp., GlaxoSmithKline and Sanofi Pasteur, with about 80 percent of the global market for seasonal flu vaccine, are separately producing and testing H5N1 vaccines.

Vaccines are also being produced by Australian, Hungarian and Chinese firms, and a consortium of Japanese manufacturers. MedImmune Inc., a biotech company based in Gaithersburg, Md., is working on a weakened live H5N1 vaccine, similar to its annual product, FluMist.

Two other companies, Baxter and Solvay, are developing pandemic vaccines using cell cultures, a technology that will eventually replace the laborious method that now requires growing virus in hundreds of thousands of fertile chicken eggs.