In a highly unusual move, two senior Agency for International Development officials have decided to break with the Reagan administration over its decision to vote at the World Health Assembly this week against international guidelines for marketing infant formula.

Dr. Stephen Joseph, AID's top health official and Eugene N. Babb, the agency's top agriculture and rural development official, have informed the White House that they plan to hold a news conference Monday at the American Public Health Association to protest the decision.

It will be one of the first times since the Reagan administration took office that any high-ranking officials have voiced their displeasure publicly with a policy decision.

The other 156 governments at the assembly, now meeting in Geneva, are expected to vote for the voluntary code.

Contacted at his home, yesterday, Babb said the vote "will be seen in the world as a victory for corporate interests" over the legitimate health concerns of developing countries.

"In my view, we [the United States] are going to look very foolish to the world," he added. "To me, it's inconceivable that our government could take this position."

"I really don't know who made the decision on this, but I think they didn't understand the full implications of what they were doing," said Babb who, like Joseph, is a career AID employe.

The code is aimed at curtailing commercial efforts to convince women in underdeveloped, Third World countries to switch from breastfeeding their babies to formulas, which in these countries are mixed with contaminated water.

About 10 million infants and young children annually suffer from sometimes fatal malnutrition and other diseases associated with inadequate breastfeeding and the use of substitutes, according to a memo prepared by D. John H. Bryant, one of the administration's top health officials.

The code is supported by religious and health groups in the United States, as well as most foreign governments. It is opposed by three U.S. formula manufacturers and the Grocery Manufacturers of America.

In announcing its opposition Friday, the Reagan administration raised legal, economic, constitutional and commercial objections to the code. Administration officials complained that the code would ban advertising and might be applied to other food products in this country.

Although conceding that breastfeeding ususally is the healthiest way to nourish infants, they argued that there is no proven relationship between marketing formula and infant health.

In its most controversial passages, the code would forbid aggressive marketing tactics such as advertising, distributing free samples, or sending nurses and non-nurses dressed in white into maternity wards and villages in underdeveloped countries to promote the use of baby formula.

Supporters of the code argue taht its provisions are non-binding and would not apply to sales of formula in the United States. They also note that the International Council of Infant Formula Industries, led by Nestle, the giant Swiss food conglomerate, has agreed to support most provisions of the proposed code.