For about $5.1 billion, the lives of 6 million children younger than 5 could be saved each year, provided the money were spent to extend proven methods of disease prevention and treatment in the world's poorest countries.

That is the estimate reached by a team of researchers in a laborious and unusually detailed effort published today in the journal the Lancet.

The investment in measures including breast-feeding education, insecticide-impregnated mosquito nets, zinc supplements and antibiotics would reduce mortality at an average cost of $887 per life saved. That is an exceptionally good bargain, at least by the economic standards of rich countries, where $50,000 to save a single year of life is considered a reasonable investment.

"How can we determine if it is affordable?" the authors ask at the end of an explanation of their calculations. "We challenge readers with some salient comparisons. For example, $5 billion is about 6 percent of expenditures for tobacco products in the USA for 2003."

In an effort to bring renewed attention to "child survival" -- which has taken a back seat to AIDS, bioterrorism and other problems in the past decade -- a group of epidemiologists two years ago developed a strategy to reduce mortality using only interventions that are low-tech, known to work and inexpensive. The new study estimates the cost of applying them universally in the 42 countries, mostly in sub-Saharan Africa, where 90 percent of childhood deaths occur.

The researchers -- who are also advocates -- hope it will get the attention of politicians as well as global health experts.

"The word on the street is: 'If you don't have a price tag, like the people pushing for HIV/AIDS treatment do, how can you expect the U.S. Congress and donors to support you?' Well, we have a price tag now," said Jennifer Bryce, the study's lead author. She is a consultant on child health issues who previously worked at the Centers for Disease Control and Prevention and the World Health Organization.

The team used the state of medical care in 2000 as the baseline. In that year, there were about 10.8 million deaths of children younger than 5.

For each of the 42 countries, the researchers estimated the percentage of children that were getting 23 different prevention or treatment services, and the cost of the services. Researchers then estimated how much more would have to be spent to provide those services to 100 percent.

The calculation assumed the additional services would be delivered by community-based health workers rather than by building hospitals and other facilities.

The projections also took into account that the incidence of illnesses such as malaria and dysentery would fall once the full package of preventive measures was in place -- and that, consequently, there would be fewer cases needing treatment.

The 16 prevention services included childbirth with a "skilled attendant" (generally a midwife); giving the drug nevirapine to prevent the transmission of the AIDS virus from infected mothers to newborns; and broader use of several vaccines. The seven treatment services included antibiotics for pneumonia and broader use of lifesaving antimalarial medicines.

The researchers' final calculation was that it would take an additional $5.1 billion each year to save 6 million lives each year. About $4.2 billion is spent annually now on the package of services they describe. If the increased expense were borne solely by the 42 countries themselves, it would cost them on average $1.23 per capita each year.

The uncertainties in the projections should not detract from the message, said Barbara McPake, a health economist at the London School of Hygiene & Tropical Medicine.

"You can't come up with a number like this without making some pretty heroic assumptions," she said of the $5.1 billion figure. "But I don't think there is a chance that they are vastly overstating or understating the estimate," she said. "It's very important to point out that this isn't expensive, and that there's an unsolved problem of huge dimensions that is relatively neglected."