Dr. Beno Sandor Vajda, 65, a pediatrician who had practiced with the Group Health Association Inc. in Washington since 1960, died of cancer Thursday at his home in Arlington.

Dr. Vajda, who got his early medical training in his native Hungary, first came to Washington in 1953 as an intern at the old Garfield Memorial Hospital. In 1955, he became a pediatric resident at D.C. Children's Hospital and shortly thereafter joined the staff of Baby's Hospital in Wilmington, N.C.

In 1956, when the Hungarian uprising broke out, he offered his services to the American Red Cross. He was assigned to Hungarian refugee camps in Austria. Back in the United States, he took a fellowship at the Children's Medical Center in Boston, and then was a researcher at the Harvard School of Public Health and at the Children's Center until his return to Washington in 1960.

In addition to his work with the Group Health Association here, Dr. Vajda was on the staffs of Children's Hospital, the Georgetown University Medical Center and the George Washington University Hospital.

He was born in Debrecen, Hungary, and earned his medical degree from the University of Debrecen in 1940. He was a medical officer in the Hungarian Army during World War II.

Dr. Vajda had been a leader of an anti-Nazi democratic political movement in his hometown. When the Communists took over Hungary in 1948, he fled to the West.

He went to Cuba, where he was a medical officer in a refugee camp. There he met Patricia Lee Minar, an American teacher, whom he married. They remained in Cuba until 1953. Dr. Vajda became an American citizen in 1957.

In addition to his wife, of the home in Arlington, survivors include a daughter by a previous marriage, Judith, of Budapest, and a sister, Ilona Khuli, of Miami. CAPTION: Picture, DR. BENO SANDOR VAJDA