A doctor who has treated more than 770 cases of children with abnormal sexual development in Puerto Rico told a women's group here yesterday that one of her young patients has developed ovarian cancer.

"One 12-year-old girl, who developed precocious puberty at age three, now has cancer of the right ovary," Dr. Carmen Saenz told the National Conference of Puerto Rican Women.

She showed the group of 110 women slides of the physical abnormalities, such as early breast development and menstruation, that she has found among her patients. The group later proposed raising money to send an epidemiologist to the island to find out the true incidence of the disorder, a public health disaster described by U.S. officials as "Puerto Rico's Love Canal.

Saenz and another pediatric endocrinologist on the island, Dr. Adolfo Perez-Comas, believe that estrogen-based growth stimulants fed to animals may promote the problem.

"It's either abuse or ignorance of the people using the cattle and poultry implants, that they are not withdrawn in time before the animals are marketed," said Saenz.

But initial studies released by the U.S. Department of Agriculture and the Food and Drug Administration have not found evidence of illegal sales of growth stimulants or high residues. A recent scientific conference on the problem concluded that more studies are needed.

One study may be undertaken by the National Institute of Child Health and Human Development, a divison of the National Institutes of Health in Bethesda.

Dr. Ora Pescovitz, a pediatric endocrinologist there, said the institute is looking for money and bed space to bring 15 to 20 of the children to the United States for examination and treatment.

"We volunteered to potentially see some of the children," said Pescovitz. "We are one of the major centers specializing in children who have precocious puberty, so it makes sense."

She said the recent budget cuts have ended NIH's practice of automatically transporting any patients whose conditions the institutes wanted to study. "Several parents did approach me in Puerto Rico saying they would come here on their own, but we don't want the study to be skewed by including only those able to pay," Pescovitz said.

She said it would take a month to determine if the money and space in the 24-bed children's unit could be found.

If the study were done, the institute would be the first federal agency to examine any of the children. A two-year study recently was completed without conclusion by the Centers for Disease Control, but it covered data taken from a selected number of patient charts.