Donald B. Watt, 84, the founder of the Experiment in International Living, a program under which youngsters live with families in foreign countries, died in Lancaster. Pa., Sunday of a heart attack following a stroke.

Dr. Watt had been moved to a nursing facility in Lancaster from his home in Putney, Vt., last week because of a stroke he suffered some months ago in Amsterdam.

He moved to Putney from Syracuse, N.Y., where he was an official of Syracuse University, in 1932, the year in which he founded the Experiment in International Living. Since its founding, the program has arranged for an estimated 250,000 young people-including 50,000 Americans-to live with families in countries other than their own. Its purpose is to foster international understanding and goodwill.

Dr. Watt summed up this purpose with the dictum: "People learn to live together by living together."

He relinquished activedirection of the Experiment in 1950. In the years since, he has devoted much of his time to teaching English to foreign students in this country and elsewhere in the world.

Dr. Watt was born in Lancaster. He attended the Lawrenceville School and graduated from Princeton University in 1916. He then went to the Middle East and served as a YMCA volunteer with British and Indian forces in World War I.

Upon his return to the United States, he engaged briefly in the management of a cement companmy in Catskill, N.Y., and then pursued graduate studies at the University of Pennsylvania and at Yale University. In 1927, he was appointed personnel director of Syracuse University.

He founded the Experiment of International Living after conducting a study of summer school programs run by the International Association of the League of Nations Society.

Survivors include his wife, Leslie Somers Watt, of the home of Putney; three children, Donald B. Watt Jr., of Putney, Leslie Barbara Seymour, of Westminister West, Vt., and Laura Phyllis Ingersoll, of Cambridge, Mass., and 10 grandchildren.