The baby food war, a good six years old, is heating up. In early May at the World Health Assembly, the United States and other governments will be asked to vote on an international code limiting the marketing practices of the major baby food companies.

It was all begun by a British journalist, Mike Muller, who in 1974 wrote a pamphlet "The Baby Killer" for the British relief agency, War on Want. It accused Nestle and other baby food companies of promoting bottle-feeding in poor countries at the expense of breast-feeding, leading to a sharp rise in infant mortality rates.

Only when the report was republished by a Swiss organization and retitled "Nestle Kills Babies" did it attract notice.

Since then, the baby formula campaign has gained increasing numbers of adherents, not only from social action groups, but from the churches, noted pediatricians, and not least from senior officials in the World Health Organization and the U.N. Children's Fund.

UNICEF's wise and perceptive executive director, James Grant, has observed that if we can "promote and protect the practice of breast-feeding, we can save 1 million infant deaths each year in the 1980s."

Perhaps this seems an extraordinary claim, but in fact the abandonment of breast-feeding in Third World countries has gone so fast that there is little reason to doubt its accuracy.

In Chile 20 years ago, 95 percent of 1-year-olds were being breast-fed. By 1975 it was down to 20 percent. Research has shown that Chilean babies who were bottle-fed during the first three months of their life suffered three times the mortality rate of those who were exclusively breast-fed.

The baby food companies in their defense say two things. First, the fall in breast-feeding is not their fault -- life styles are changing all over the world. Women want to work and want a substitute for nursing.

Second, they say, they have become increasingly careful about their promotional techniques, admitting in a kind of backhanded way that the criticism ranged against them has had some impact.

But to what extent are life styles changed by commercial pressure? It is difficult to be precise, although one can assume that the companies would not waste their money on advertising if it did not show some return. The fact is that the infant formula companies package and promote their product in shops, nurseries, clinics, hospitals and in the media in such a way that women of poor countries struggleing to be emancipated and modern are easily swayed.

It's not difficult to understand -- women in industrialized countries went through this experience themselves only a generation ago. Now the pressures are working the other way and in Britain, for example, 63 percent of mothers breast-feed, more than double the proportion 10 years ago. Western mothers are now being told firmly and strongly by their doctors that breast milk is best, more nourishing and confers protection from viral and bacterial attack.

These are all good reasons for cutting down the pushing of brightly presented alternatives in the Third World, where health education is much less developed than in the industrialized countries.

In October 1979, WHO and UNICEF convened a special meeting on infant feeding which recommended an end to various marketing approaches. In practice the 1979 recommendations have too often been ignored.

One wonders why the companies go on, despite the criticism. The fact is it is a highly competive $2 billion a year business and as European and North American mothers go back to breastfeeding, new markets have to be found.

This is why the WHO-UNICEF mandatory code is needed. And once it is passed, governments need to legislate to make sure it is enforced.