The parents of a 6-year-old girl critically disabled shortly after her birth have won a $1.1 million court settlement from the National Naval Medical Center in Bethesda. The child developed epilepsy, brain damage and other disabilities after a blood transfusion malfunction went undetected for a critical period after she was born.

The settlement, one of the largest of its kind against the federal government in recent years, went to Gary and Diana Stetler, formerly of Gaithersburg, on behalf of their daughter, Sonya L. Stetler.

Sonya was born Dec. 20, 1976, by cesarean section at the medical center, where doctors had been alerted in advance that mother and fetus had incompatible Rh blood types that would require the baby to undergo a series of so-called double exchange transfusions to replace her entire blood supply.

Four exchanges were performed in the first few days of the child's life but, according to Stetler family attorney Robert R. Michael, a catheter used to introduce fresh blood into the child's body was not removed as required by hospital policy. Further, he said, monitors to detect abnormal heart rate and respiration had been turned off, probably sometime on Dec. 25.

Shortly after midnight on Dec. 26, Michael said, a valve controlling the flow of blood into the child broke loose from the catheter, and blood poured out of the child through the catheter. Since the monitors were not turned on, Michael said, the malfunction was not noticed for a few minutes until a nurse discovered a pool of blood forming under the child's Isolette.

There were further delays, Michael said, until an emergency pediatric team arrived to stabilize the situation. By then, he said, the baby had lost 50 percent of her blood and as a result developed brain damage, epilepsy, mild cerebral palsy, total deafness in one ear and partial deafness in the other.

The Stetlers unsuccessfully sought administrative relief through the Navy, then filed a lawsuit against the hospital in 1981 in federal court in Baltimore, claiming the child was permanently disabled by the negligence of the hospital. Michael said the child now has severe speech and motor control problems. Her epilepsy is controlled by medication, he said.

The case went to trial last May 23, and at the end of the first day of testimony, government attorneys offered to settle for $1.1 million.

Because of the size of the amount, the settlement had to be cleared by several Justice Department officials including Assistant Attorney General J. Paul McGrath, chief of the civil division, who gave his final approval in June. Checks to the Stetlers and Michael totaling $1.1 million were issued last week. Under the Federal Tort Claims Act, Michael and a second attorney, who assisted him briefly, receive 25 percent of the settlement, or $275,000.

The Stetler portion of the settlement, Michael said, will be used for the child's occupational and speech therapy and to compensate her for income she cannot expect to earn as an adult. "We are well pleased," Michael said.

Steve Allen, assistant U.S. attorney representing the government in Baltimore federal court, described the $1.1 million as a "fair settlement arrived at with any eye to providing for that child's future needs."

The Stetlers are separated. Diana Stetler, who has custody of Sonya, lives in Missouri. Gary Stetler, an E6 medical corpsman in the Navy, lives in Florida.