The Reagan administration has been advised by one of its top health officials to endorse a proposed strict international code for ethical marketing of infant formula and other breast-milk substitutes.

But, in a bow to three American formula manufacturers that have been lobbying against the code since mid-March, the official also suggested that the United States voice its concerns about provisions "that are troublesome in our domestic context."

The recommendation was made by Dr. John H. Bryant, deputy assistant secretary for international health in the Department of Health and Human Services, to HSS Secretary Richard S. Schweiker. The Washington Post obtained a copy of Bryant's six-page memo, which went to Schweiker a month ago. He has not made a decision on it, an aide said yesterday.

The World Health Assembly is expected to take up the draft code May 18. But the American delegation has gone to Geneva uninstructed because an interagency group led by Bryant and the State Department's John W. McDonald Jr. failed to agree on a U.S. position in several weeks of discussions. A State Department press aide said a decision may not be reached before the assembly opens tomorrow.

The code, which would be purely advisory, is supported by nearly all the 156 member-nations of the World Health Organization, as well as by the American Public Health Association, a coalition of religious and other groups and pending House and Senate resolutions. The Senate resolution, cosponsored by three Republicans -- Mark O. Hatfield (Ore.), John C. Danforth (Mo.) and Bob Dole (Kan.) -- warns "it would be detrimental to our national and international interests" for the United States to object to adoption of the code.

By contrast, Ernest W. Lefever, acting assistant secretary of state for human rights, contended in a Wall Street Journal article Jan. 14 that the code "would do little to advance infant nutrition in the Third World." He attacked "anti-industry activists, U.N. bureaucrats and their allies" for seeking a "hobbling" through "international regulation" of the multinational corporations that sell formula.

Code supporters say it will be a shield, mainly in Third World countries, against promotional practices that have led mothers to forsake or curtail breast-feeding -- which undisputedly provides the best nutrition and protection against infection -- in favor of substitutes that often are mixed with contaminated water.

About 10 million infants and young children suffer annually from sometimes fatal malnutrition and other diseases associated with inadequate breast-feeding and use of substitutes, the Bryant memo said. James Grant, director of UNICEF (United Nations children's fund) says promoting and protecting breast-feeding "can save 1 million infant deaths each year in the 1980s."

Bryant's memo reported "particularly strong feelings among European and developing countries that any weakening of the code is unacceptable." The State Department press aide declined to comment on reports that other western nations, replying to State Department inquiries, told the United States they would refuse to go along with any U.S. opposition to the draft code.

Bryant's memo also made a surprise disclosure that may be embarrassing to Lefever, partly because of his Journal denunciation of the WHO code. He coupled that denunciation with praise for a mild voluntary alternative adopted by the International Council of Infant Formula Industries. ICIFI, led by Nestle, the giant Swiss-based food conglomerate, "has informed the U.S. mission in Geneva that it is prepared to accept the [WHO] code in its current form," Bryant wrote.

ICIFI is led by an executive of Nestle, the largest formula seller outside the United States. Last year, Nestle gave $25,000 to the Ethics and Public Policy Center, a Washington think tank of which Lefever was president and U.N. Ambassador Jeane Kirkpatrick a director.

Also in 1980, the center circulated a Fortune magazine article labeling church groups and other Nestle boycotters "Marxists marching under the banner of Christ." Both Lefever and Nestle deny any connection between the donation and the center's circulation of the article.

The center also received $10,000 from Bristol-Myers Co., whose Mead Johnson subsidiary sells formula here and abroad. Mead and Ross Laboratories, owned by Abbott Laboratories, have never joined ICIFI; instead, each adopted a stricter individual code than the association's. Mead and Ross sell mostly in the United States, which accounts for only about $2 billion in worldwide formula sales. ICIFI's only U.S. member is Wyeth Laboratories, owned by American Home Products Corp.