Countering decades of promoting "breast is best" for infant nutrition, the United Nations is issuing recommendations intended to discourage women infected with the AIDS virus from breast-feeding. The much-debated step aims at preventing transmission of HIV, the AIDS virus, from mothers to babies in what U.N. officials say is "a runaway epidemic" in many developing countries.

Last year, breast-feeding accounted for up to a third of the 600,000 children in the world who became HIV-infected, said Dr. Bernhard Schwartlander, the chief epidemiologist for UNAIDS, one of the U.N. agencies that issued the recommendations.In its directive, the United Nations said it was deeply concerned that advising infected mothers not to breast-feed might lead many noninfected mothers to stop breast-feeding. To reduce such chances, the agency is advising governments to consider bulk purchases of formula and other milk substitutes and to dispense them mainly through prescriptions.

The compelling reason for the action is the soaring HIV infection rates in much of the world, said Tomris Turmen, a U.N. official. As many as 70 percent of women at a prenatal clinic in one city in Zimbabwe and 30 percent of women in major urban areas in six African countries were found to be infected in recent surveys.

Nevertheless, the recommendation is controversial. In desperately trying to deal with a crucial aspect of mother-to-child transmission of HIV, the United Nations is running up against a fundamental, even ideological, pediatric practice. It also risks stirring memories from decades past, when international corporations promoted formula, and many babies died when it was mixed under unsanitary conditions.

The new U.N. policy has emerged after years of internal debate. Merging the two complex problems of AIDS and breast-feeding has created arguably the greatest labyrinth of ethical and practical issues AIDS workers have faced. Debate over breast-feeding for HIV-infected women has been as emotional as scientific.

Dorothy Odhiambo of Nairobi, Kenya, a representative of African nongovernmental organizations, said at the recent 12th World AIDS Conference in Geneva that "it becomes unethical to continue not to do anything about it knowing very well that children are getting infected daily."