Patricia and Julian Cawthorne say they have spent 14 years trying to get an answer from Johns Hopkins Hospital about what went wrong during heart surgery on their 6-year-old daughter in 1971. Karen Lee Cawthorne emerged from the operation with severe brain damage, and to this day, at age 20, has the brain function of a toddler.

The Cawthornes brought Johns Hopkins and the nationally known chief of its pediatric surgery department to court this week in a $20 million malpractice lawsuit. They say that their daughter's condition resulted from a lack of oxygen to the brain during and after the surgery.

The trial, which began Tuesday in U.S. District Court, pits a working class couple from Lynchburg, Va., against a renowned hospital wanting to protect its reputation. During the legal proceedings, Hopkins officials have said that the hospital could not locate key medical records pertaining to this case and that they could not identify the anesthesiologist who took part in the operation. Today, Hopkins won a gag order from District Court Judge J. Frederick Motz that restrains lawyers from talking about the case to the media.

The Cawthornes and their lawyers have said in court that Hopkins' failure to produce the records is an effort to cover up its mistakes and shield it from legal liability. Hopkins officials deny those allegations, and say that what happened to Karen Cawthorne was unusual and unpreventable.

Today, Dr. Gilbert Riberio, a Fairfax anesthesiologist subpoenaed by the plaintiff's attorney N. Roy Grutman, took the witness stand and acknowledged that he administered anesthesia to Karen Cawthorne in 1971. In a sworn deposition prior to the trial, Riberio had said he did not know who administered the anesthesia.

Riberio, a second-year resident at the time of the operation, acknowledged his role in the case after Grutman entered into evidence a hospital operating room log that lists doctors and nurses involved in the operation, including Riberio.

"I will accept that I was the anesthesiologist in this case on that basis," Riberio said after viewing the log.

The surgeons named in addition to the hospital in the lawsuit are Dr. J. Alex Haller Jr. and Dr. William B. Iams, who was assisting Haller. The surgery, which involved a cardiopulmonary bypass, was meant to correct a congenital heart defect.

Haller, a well-known pediatric surgeon, was featured several years ago in a segment of NBC's "Lifeline" series about the medical profession. The series has since been rerun on public television.

Hospital spokeswoman Elaine Freeman said today that Hopkins believes that Karen Cawthorne's brain damage was caused by clots or air bubbles that restricted the flow of oxygen to the brain.

According to the lawsuit, the surgery left Cawthorne profoundly retarded and spastic. Her father, a forklift operator, and her mother, a preschool teacher, have been unable to care for her and she has been in institutions since the operation.

In testimony today, Lottie Cole, medical records administrator at Hopkins, said that her office has received at least six requests from institutions for Karen Cawthorne's medical records. She said that while some portions of the records were located and fowarded to those who requested them, some documents were missing from the files.

The Cawthornes contend that key records are missing on the surgery itself and on followup intensive care treatment. Those records, they say, would show what caused their daughter's brain damage.