THE PROPOSAL being made in the World Health Organization that member governments restrict the marketing of infant formula, to encourage breast-feeding, is a tough one for this country and especially for this administration. The proposed code, sanctioning interference in the domestic marketplace to restrict the promotion of a legal product, cuts across the grain of a free-enterprise society and of an administration with a strong anti-regulation bent and -- if the truth be told -- of a newspaper that lives off advertising. That some part of the anti-formula effort arises from ideological antagonism to multinational corporations makes support of the code even more distasteful. It is understandable why the Reagan administration, inheriting a pro-code position, is contemplating a revision of American policy.

It is important, however, to grasp what is behind the anti-formula campaign, which is worldwide. Some part of it unquestionably does arise from political quarters unfriendly to multinationals and to Western capitalism. As it happens, this part has been extensively publicized in the United States, most recently in connection with the appointment to a State Department post of Ernest Lefever, who as a private citizen vigorously joined that battle. He says, by the way, he is not taking part in current government deliberations on the WHO code.

The anti-formula campaign remains in essence a health issue. Study after study shows that infant formula, in the imperfect and unsanitary conditions commonly found in the Third World, is bad for babies' health. Formula requires clean water, or the means to sterilize water and bottles or to refrigerate the mixed formula, the money to buy enough formula so as not to have to overdilute it, and the information and training to manage the formula process. Breast-feeding, by contrast, works for all but a small percentage of women, even the undernourished. Typically, a malnourished woman would not have the money to buy formula anyway. Cow's milk is often a superior substitute. That is why experts would keep formula available but would expect it to be used by particular groups of women. Medical testimony puts the number of children's lives that could be saved each year by a return to breast-feeding at a million and upward.

Third World health professionals deplore the trend anyway from breast-feeding, but often they cannot counter commercial pressures. Students of American tobacco know the problem. Those professionals and their political allies are in effect trying to make an end run. They would not try to ban the export or sale of formula, but they would use the international network to apply moral pressure on the marketing activities -- advertising, free samples, women in nurse-like dress peddling door to door, etc. -- of the foreign formula companies. For, though changing life styles doubtless tell, marketing has been shown to help move women off breast-feeding. Switzerland's Nestle is the leader in this $2 billion-a-year global business. Sales by American firms -- Abbott/Ross Labs, Bristol Myers/Mead Johnson and American Home Products/Wyeth Labs -- are put in the scores of millions of dollars.

The administration is being compelled to balance its strongly felt ideology and the clearly expressed interests of a business constituency against the dimly perceived health needs of foreign countries, many of which are not particularly sympathetic to some of the administration's other policies. But can it do anything but go with the babies?