The World Health Organization will announce today in Tanzania that it will spearhead a program to reduce death from malaria by increasing 30-fold the use of insecticide-impregnated mosquito nets in Africa.

The five-year program will seek to boost both supply and demand for bed nets by subsidizing local manufacture and increasing people's understanding of their usefulness. Although some very poor households will probably get nets for free, the strategy is to use market forces, rather than charity, to promote their spread.

Studies conducted in numerous sub-Saharan countries in the last decade have shown that when children sleep under the nets, mortality falls by about 25 percent.

Worldwide, malaria kills about 1.1 million people each year, about 700,000 of them African children under the age of 5. Of all deaths of children every year, about one in 14 is an African who dies of malaria.

"It's a huge piece of the child mortality pie globally. This program is likely to have an enormous impact on that," said Nils Daulaire, head of the Global Health Council, a Washington consortium of international health organizations.

WHO officials estimate that about 60 million of sub-Saharan Africa's 120 million child-containing households are in regions where malaria is endemic and bed nets might prove useful. Only about 2 million households, however, are now using them.

The nets cost $4 to $6 but are not widely available. They must be re-treated with a pyrethroid insecticide every six months, at a cost of about $1. Although the chemical kills some mosquitoes on contact, its main function is as a repellent that prevents insects from finding their way through holes that inevitably appear in the nets.

The British government will commit $70 million to the program, a spokesman for the Global Health Council said. The U.S. Agency for International Development (AID) recently committed $15 million to pay for market research and bed net promotion--services that presumably will encourage local manufacturers.

Nigeria in West Africa and Kenya, Tanzania, Uganda and Zimbabwe in East Africa are the most promising immediate targets, said John W. LeSar, head of the international health programs for the Academy for Educational Development, a nonprofit organization in Washington that will do the work for AID.

A recent study in Ghana found the country has about 9.5 million beds (roughly three per household) that could theoretically be fitted with a net. About half of all Ghanaian households now buy something for mosquito control. (Often, this is a slow-burning repellent used at night.) From 15 to 35 percent of households might invest in nets during the first year of a campaign, researchers found.

In some endemic areas, children are bitten by several malaria-transmitting mosquitoes each night, LeSar said. Nets not only decrease deaths from malaria, they reduce the nonfatal effects of the disease (notably chronic anemia) that make children susceptible to other infections.

In a study of five regions of Gambia that had a total population of 116,000 people, use of impregnated nets reduced mortality in children aged 1 to 9 by 25 percent. (A little more than half the reduction was in malaria deaths.) Other, more targeted programs have produced mortality reductions of up to 60 percent.

Cost is a barrier in some places. In a Gambian study, only 14 percent of nets were re-treated when an insecticide give-away program was stopped. In one study, frequent washing of nets soiled by children shortened the repellent action significantly.

In addition, insecticide-resistant mosquitoes have been found. Use of nets, however, is less likely to promote resistance than the spraying of chemicals whose main purpose is to kill, rather than repel, mosquitoes.