A little-noticed but emotional battle is now going on within the executive branch of government over U.S. support -- or lack of it -- for a new international code to curb a practice that kills Third World babies.

The practice is the over-promotion of commercial infant formulas to African, Asian, Caribbean and Latin American mothers who then abandon breastfeeding. Instead, they use, and frequently misuse, the formulas, resulting in infant illness and deaths.

The federal struggle has pitted the State Department against health and foreign aid agencies.

State Department officials say they fully agree with the need to regulate the multinational firms who often place the glossy ads for their "convenient" formulas on the walls of Third World nurseries.

Health, foreign aid and Peace Corps officials all think that the department gave the United States a black eye at a recent World Health Organization meeting by trying to block speedy drafting of a proposed code by the WHO secretariat, and to substititute negotiations that would include the manufacturers of baby-formulas.

Sam Brown, director of Action (parent agency of the Peace Corps), told State that its "go slow" policy lent support to the manufacturers' desire to resist any change.

Other officials disagree on whether or not this has been the department's unstated agenda. But many feel that the United States should listen to all parties, including producers, then help make a policy that is best for the people of the Third World, not for a company or group of firms.

Third World mothers do not always have a good breast-milk supply. Increasingly, many must work, making it harder for them to breast feed. Inspired in part by the seductive posters of firms like Nestle, Abbott, Mead Johnson, Wyeth and others, thousands now use powdered substitutes.

According to testimony by public health experts, many mix the substitute with unsafe water, or use unclean bottles. Or they let the mixture spoil for lack of refrigeration. Or because of the cost, they put too little in the water.

Last October U.S. Agency for International Development (Aid) and health officials took part in a 23-nation WHO-Unicef technical conference that agreed on the need for a marketing code and asked WHO to prepare one.

Conferees agreed that product marketing should not discourage breastfeeding. They said there should be no promotion to the public of formulas or feeding bottles. They said firms should stop giving doctors and clinics too many free samples to start infants on formula. And they said the makers' personnel should not be allowed to work in under-developed nations' health systems.

In March, Washington lawyer and former undersecretary of state William D. Rogers visited the State Department on behalf of American Home Products Corp. and its formula-making subsidiary, Wyeth International. E. Steven Bauer, Wyeth vice president who accompanied him, declines to discuss what he and Rogers said. An informed source said that Wyeth asked State to try to remove the issue from a WHO agenda for discussion in May.

In congressional testimony last February, American Home Products agreed that there should be no formula advertising to the Third World public. But the company's executive vice president, John Stafford, said that use of samples was a decision local doctors should make, and any Wyeth-paid personnel in local health departments were there to do research.

The State Department also listened to activist, often church-sponsored, groups who decry all such activities as blatant sales promotion.

But at an April meeting at State, Donald Green, special assistant to Action's Brown, complained that the United States has not yet recognized that some firms' practices are "harmful and immoral." Brown told the department by letter on April 22 than "industry is seeking to delay and undermine" action, and "we have not yet developed" a policy.

Without consulting other agencies, State pressed ahead with efforts to make drafting a code the subject of intermentional negotiations.

At the annual World Health Assembly in Geneva in May, an unprepared U.S. delegation was stunned by a sudden damand from State Department officials in Washington that they seek two such amendments to a Swedish resolution that called for accepting the October recommendations and directing WHO officials to work on a code to be voted on next May.

If the U.S. amendments failed, said State officials, the result might be "an unacceptable document" that might not "take U.S. interest into account." "

In reply -- according to documents obtained by The Washington Post -- the delegation twice wired Washington that the U.S. attempt was seen by other nations as "an attempt to undermine, stall and delay efforts to deal with improper marketing."

Dr. John Bryant of the Department of Health and Human Services, who was the leader of the delegation on this issue, introduced the amendments, as ordered. But he told the assembly: "It is with the greatest of reluctance that my delegation does this," and "I apologize to my colleagues for bringing this matter up."

At 7 a.m. one morning a disturbed HHS Secretary Patricia Roberts Harris telephoned Deputy Secretary of State Warren Cristopher to protest State's stance.

A week later an equally disturbed Martin Forman, AID nutrition head, wrote John McDonald, the responsible officer at State: "I fear that U.S. credibility . . . has now been dealt a severe blow by [State's] unilateral action . . . to pursue a hard line on a matter of United Nations process while neglecting the overriding principles involved."

Once its amendments were defeated overwhelmingly, the United States finally joined 35 other nations in Geneva in supporting the Swedish resoltion.

Today, Harris Forman, Bryant and the State Department's Neil Boyer, a delegate to the assembly, agree that the department was following the procedure it favors in drafting other international codes. Bryant explains that he apologized simply for introducing new amendments after having agreed to the earlier plan.

Harris says that, starting with an interagency meeting next tuesday, "we of HHS will exert our leadership" to curb overpromotion of what can "in the wrong milieu be a killing substance."

What the United States finally does, and how quickly it permis WHO action, will be the test.

Jamaica has banned public advertising of the breast milk substitutes. Socialist Algeria imports them only in bulk and distributes them through government programs. Papua New Guinea requires a doctor's prescription to buy even a feeding bottle or nipple.

Many executives of firms that sell the products say that they, too, believe in responsible sales practices.

The International Baby Food Action Network, one activist group, has collected information and photos that it says show 202 violations of the October recommendations between January and April 1980.

The photos show posters for the formulas in maternity wards and pharmacies, calling breast-milk substitutes the "best" food for babies, as well as numerous other examples of continuing hard-sell tactics.