One of the biggest events of the Atlanta social season will be next month's wedding of Mayor Andy Young's 30-year-old daughter Andrea Idelle to Dr. A. Knighton Stanley, pastor of the People's Congregational United Church of Christ here. Andrea, the oldest of Young's four children, is a graduate of Swarthmore College and the Georgetown University law school. For the past two years she has worked on Sen. Edward Kennedy's legislative staff and traveled with him on his trip to Africa in December.

Stanley, 48, the divorced father of two children, 18 and 20 years old, has been pastor of the People's Congregational Church here for 18 years and teaches at Howard University's Divinity School. He was director and special assistant to then-mayor Walter Washington's bicentennial commission and there was once speculation he might himself run for mayor of the District. When asked yesterday when he had met Andrea, Stanley said, "I've known the family and have known her all of her life."

Stanley said about 1,500 are invited to the Aug. 10 wedding and reception following in Atlanta's city hall. After the wedding, Andrea will live in New York City, where she will be an executive for the African region with the United Church World Board, United Church of Christ, and will commute to Washington on weekends. It is her first marriage.