Alva Myrdal, 84, who won a 1982 Nobel Peace Prize for her tireless efforts as an advocate of world disarmament and who also was a learned and compassionate voice in the fields of education, women's rights, and social welfare, died Feb. 1 in a hospital in suburban Stockholm. She underwent an operation in 1984 for a brain tumor, and also had a heart ailment.

She was the wife of Gunnar Myrdal, a cowinner of the 1974 Nobel Memorial Prize in Economic Science, whom she married in 1924.

Over the years, she had served at the United Nations, was Sweden's ambassador to India, had served as a Social Democrat in the Swedish parliament, and as minister of disarmament and church affairs in the Swedish cabinet. As a teacher and writer, she had a profound influence on the debate surrounding her country's pioneering efforts in social welfare.

The citation for her Nobel Prize, which she shared with Mexican diplomat Alfonso Garcia Robles, said that she had opened the eyes of the world to the threat of the arms race. Her other awards included the first Albert Einstein Peace Prize in 1980.

Mrs. Myrdal attracted international attention from the moment in 1961 when she made a plea for the implementation of a nuclear test ban treaty in her first speech as Sweden's delegate to the United Nations disarmament conference in Geneva.

As the years went by, Mrs. Myrdal became increasingly critical of both the United States and Soviet Union for what she saw as their unwillingness to work seriously and sincerely for disarmament.

"The actions of those who lead the superpowers are governed by a deep lack of reason and common sense," she said after winning the Nobel Prize.

After learning of her death, Swedish Prime Minister Olof Palme paid tribute to her work in fields as diverse as child care, women's liberation and disarmament.

"Alva devoted the last decades of her life mainly to the struggle for peace. With her unique perseverance and will to fight, she gave hope and confidence to those in despair over the madness of the arms race," Palme said in a statement.

Mrs. Myrdal's career was as long as her public interests were wide. If she is best known today for her recent work in foreign affairs, she originally gained prominence in the 1930s for her work and writings dealing with sociology and education.

She and her husband were coauthors of the landmark 1934 "Crisis in the Population Problem," a book that, while advocating population planning, also warned Swedes of their falling birthrate. The Myrdals also propounded the theory that the state was ultimately responsible for the care of children. This, and other writings, helped lay the foundation for Scandinavia's advanced welfare states.

From 1936 to 1948, Mrs. Myrdal was director of Sweden's Training College for Nursery and Kindergarten Teachers, which she had helped found. During her years as director, she wrote on the problems of urban children and the importance of proper toys in child development. She also served on Swedish Royal committees dealing with such issues as day care.

In 1949, she joined the United Nations, becoming head of its Educational, Scientific and Cultural Oraganization's social sciences division. In 1955, she went to India as Sweden's first woman ambassador. During her four years in New Delhi, she both developed a close friendship with the late Jawaharlal Nehru and received high marks from conservative Swedish business groups who initially had reservations concerning the woman socialist.

In 1961, she became a special assistant on disarmament to Sweden's foreign minister. She entered parliament in 1962, and four years later became the third woman to sit in a Swedish cabinet. She held both the disarmament and church affairs portfolios until retiring in 1973.

Born Alva Reimer in Uppsala, Sweden, on Jan. 31, 1902, she grew up in a middle-class and socially conscious home. A sociologist by training, she was a 1924 graduate of Stockholm University and earned a master's degree at the University of Uppsala. She also had studied in London, in Geneva, in Leipzig, Germany, and in this country.

During a 20-year teaching career, Mrs. Myrdal was an advocate of feminist causes. She was vice chairwoman of the International Federation of Business and Professional Women from 1938 to 1947, and chaired the federation's Swedish chapter for seven years.

In addition to her husband, of the home in Djursholm, Sweden, her survivors include a son, Jan, of Mariefred, Sweden; two daughters, Sissela Ann Bok of Cambridge, Mass., and Kaj Foelster of Goettingen, West Germany; eight grandchildren, and several great-grandchildren.