The National Institutes of Health have begun a study of whether babies fed two kinds of deficient infant formula suffered lasting brain damage or developmental problems.

The study is prompted, in part, by the mounting concern of doctors and parents that some of the infants who were fed the soy-based formulas, NeoMull-Soy and Cho-free, may have suffered subtle retardation, particularly of speech.

The two formulas contained dangerously low levels of a vital nutrient, chloride. Before they were recalled by the manufacturer, Syntex Corp., last August, they were fed to some 20,000 American infants. The recall began after doctors reported that some babies on the formula refused to eat, developed blood abnormalities and stopped growing normally.

In 139 of the babies, blood abnormalities were documented by tests, accordings to the most recent count from the federal Center for Disease Control. But center officials and mothers who formed a parents' lobby here have received reports of scores of other infants with growth and feeding problems that disappeared when the babies were given other food.

The formulas' deficiency moved the House of Representatives to pass a bill last May that would set nutrient levels for infant formula and require testing before a formula could be marketed or its ingredients changed. A similar Senate bill is scheduled to be voted on next Thursday by the Labor and Human Resources Committee.

But Lynne Pilot, a mother of one of the affected infants, said the bills were inadequate because they do not require manufacturers to measure nutrient levels regularly.

Pilot believes the proposed law would not prevent future formula deficiencies from occuring. "Somebody has to have a stick held over their heads," she said.

Pilot's son Bradley, now 17 1/2 months old, was tested at NIH last April -- one of 50 babies who will be studied for at least five years to determine the health consequences of the formulas. She said he scored in the bottom 10 percent on tests of coordination, even though by the time he was tested he had been off the formula for several months and had made rapid progress. She said he is now in two special schools.

"He didn't do anything until he was a year old," Pilot recalled. "He sat up and stood up and crawled around his first birthday."

The babies being studied had blood abnormalities and growth problems while being fed Neo-Mull-Soy or Cho-free, according to Dr. Van S. Hubbard, the NIH physician who heads the project. He said the children will receive physical, neurologic and psychiatric exams, and detailed laboratory tests while on diet containing a low, but adequate, amount of chloride.

He said testing the affected children's responses to a low-chloride diet may help determine why only certain babies became severely ill on the formulas.

The development of the babies in the study will be checked annually and compared to that of their siblings and babies fed other soy-based formulas.

He said the search for abnormal development stems from reports from pediatricians that some babies fed the formulas are growing more slowly and talking later than normal. But he said the babies, most of whom are now between 1 and 2 years old, are at "the hardest age to examine because variability is greatest."

If some babies suffered retardation, research suggests it may be because chloride deficiency triggered high levels of the hormone angiotensin. Studies in rats indicate that high angiotensin levels may block the brain's chemical pathways, affecting memory and learning.

Hubbard said this theory does not explain why apparently only a minority of the 20,000 babies fed the formulas suffered problems.

"I think it was a combination of how much other food the infant was taking -- or perhaps something in the (affected) child himself that made him more sensitive," he said.