Three major pediatric groups have declared that breast feeding is a "right" of mothers and that American doctors and hospitals should take steps to encourage use of it instead of commercial baby formulas.

The societies are, in effect, endorsing the key provisions of a controversial marketing code for infant formula adopted by the World Health Organization last May over U.S. opposition.

The WHO code seeks mainly to curtail formula use and discourage over-aggressive formula marketing and advertising in developing nations. The pediatricians are saying that the same kind of effort is needed to promote breast feeding and limit formula use in the United States.

Employers, they say, should provide facilities or time so working mothers can breast-feed. Hospitals, they say, should not give free samples of formula--obtained from manufacturers--to all mothers, and formula advertising and promotion should be directed at health professionals, not at the public.

While 17 to 25 percent of American mothers breast-feed for an appreciable time, "probably 75 percent" could and should for their babies' health, two main advocates of the new statement--Dr. Pearay Ogra of the State University of New York at Buffalo and Dr. Harry Greene of Vanderbilt University--said in an interview yesterday.

"We have always backed breast feeding, but we have never before come up with such a firm set of recommendations," Ogra added.

In the last 10 years, he and Greene said, scientists have learned many new things about the ways breast milk protects infants from disease and promotes health.

"You can prepare a formula with everything a child needs to grow, everything we know about," Greene said, "but there are other things in the milk, defense mechanisms, that we still don't fully understand."

The new statement was first adopted by the executive board of the American Academy of Pediatrics--the nation's practicing baby doctors--in January and will be published in this month's issue of Pediatrics, the academy's journal.

This week the statement was unanimously adopted at membership meetings here of the Society for Pediatric Research and the American Pediatric Society, scientists and professors involved in child-disease research.

The pediatricians' statement recommends that:

Doctors educate mothers and health workers on the best ways of either breast feeding or formula feeding, in cases where breast feeding is impossible or a mother wants to use formula.

Hospitals make breast feeding the "standard" method for new mothers, unless a mother decides otherwise.

Hospitals use "rooming in" periods--when the baby is in the mother's bed or nearby, rather than in the nursery--to help educate mothers and solve any breast-feeding problems.

"Mass distribution of free sample packs of commercial formula" to every mother be discouraged in hospitals.

Doctors and other health workers consider a mother's finances before encouraging use of formula. This is because many poor mothers start use of formula, then can't afford to keep buying it and substitute less healthy foods, Ogra and Greene said.

Advertising and marketing practices be carefully monitored in the United States and elsewhere "to safeguard the right to breast feed and prevent potentially unfair or unethical formula promotion."

Employers and, where necessary, legislatures act to make it possible for nursing mothers to breast feed in workplaces and public facilities.

In Atlanta, Robert Gelardi, executive director of the Infant Formula Council, representative of the main American formula makers, saw "no problem" with most of the recommendations.

But he emphasized every doctor's and mother's right and need to make an individual decision.

He said the council backs breast feeding as best for most mothers, and opposes advertising that discourages it.