A Prince George's County circuit court jury yesterday ruled in favor of a Riverdale doctor who had been sued for malpractice by a woman claiming the physician had misdiagnosed her son's spinal meningitis.

The doctor, Clarence L. Purdy, 67, said outside the courtroom that the decision vindicated him. "It means that I treated the patient adequately and without any negligence."

In the suit, Mary Ann Bernhardt, also of Riverdale, alleged that Dr. Purdy had failed to detect spinal meningitis in her 18-month-old son, David. She said that as a result her son had suffered brain damage.

According to Bernhardt, her son first saw Dr.Purdy in January 1974. The infant had a high fever. Purdy diagnosed the patient as having a respiratory ailment. Five days late, Bernhardt said she took her son to a second physician who diagnosed David Bernhardt's ailment as spinal meningitis and ordered him rushed to Prince George's General Hospital.

The woman, who had asked for $1 million in damages, argued during the six-day trial that Purdy should have detected the spinal meningitis earlier, and that the delay caused her son's brain damage. "The kids and I had to get down on the floor and teach him to crawl again," Bernhardt said.

Lawyers for Purdy -- who said he practiced medicine in the county for 35 years -- argued that the spinal disease had developed after Purdy made his original diagnosis. "There was no improper care rendered by Dr. Purdy," his attorney stated. "David's future is bright and beautiful."

David, a second-grader at Templeton Elementary School in Riverdale, is still reading at a pre-first grade level, according to his father.

The case, heard by Circuit Court Judge Jacob S. Levin, was the second major malpractice case in the county during the last two weeks. Last week, a jury returned an $800,000 malpractice award against a Silver Spring doctor.