Ida Pruitt, a writer and medical social worker who trained China's first modern caseworkers and spent her life promoting Chinese-American understanding, died July 24 at Presbyterian-University of Pennsylvania Medical Center in Philadelphia. She was 96 years old.

Miss Pruitt, the daughter of Southern Baptist missionaries, was born and grew up in China, spent nearly half her life there and, in addition to her social work in the 1920's and 30's, aided the Chinese resistance movement after the occupation by Japanese troops in 1937.

From 1939 to 1959, she lived in New York and was executive secretary of the Chinese Industrial Cooperatives, an international organization that raised funds for the creation of small producers' cooperatives in China.

In 1959, Miss Pruitt was invited to visit China as a guest of the People's Republic, which she had long supported. The State Department lifted her passport but she went anyway, according to Dr. King, and, after returning, joined a lawsuit by the American Civil Liberties Union to get her passport back. She frequently visited China, most recently in 1972.

Books Published

Her extensive writings included three books published in the United States - ''A Daughter of Han: The Autobiography of a Chinese Working Woman,'' 1945, the transcription of conversations over several years with a peasant woman; ''A China Childhood,'' 1978, her autobiography, and ''Old Madam Yin: A Memoir of Peking Life,'' 1979.

''Miss Pruitt has interpreted and mediated between Chinese and Americans as few others have been in the position to do,'' said Dr. Marjorie King, an assistant professor of humanities and social science at Hahnemann University in Philadelphia, a biographer and friend of Miss Pruitt.

Born in Penglai, on the coast of Shandong, in 1888, Miss Pruitt grew up in an inland village where for many years hers was the only Western family. Her early education was provided at home by her mother.

Coming to the United States before World War I, she studied at the Teachers College at Columbia University and, in 1918-19, worked at the Philadelphia Society of Organizing Charities. In 1920, she was chosen by the Rockefeller Foundation to establish the Department of Medical Social Work at the new Peking Union Medical College Hospital.

Trained Social Workers

From 1921 to 1939, as chief of social services at the hospital, she mediated between Western physicians and Chinese patients and trained China's first generation of social workers. One of her students, Louise She, was instrumental in establishing professional social work in Hong Kong.

Miss Pruitt's home in Peking - a traditional Chinese compound - was a meeting place for scholars, students, government officials, business people and travelers in the 1930's, and after the Japanese occupation in 1937 it became a safe house for members of the resistance movement.

In 1939, she returned to the United States to become the executive secretary of the Chinese Industrial Cooperatives. In the 1940's and 1950's, she was the organization's chief American spokesman and fund-raiser.

Miss Pruitt is survived by two adopted daughters, Kuei-ching Ho, of Saskatoon, Saskatchewan, Canada, and Tanya Wahl, of Swarthmore, Pa.