Paulo Padilha Vidal, 54, the Brazilian ambassador to the Organization of American States in Washington since 1974, died of cancer Sunday at Georgetown University Hospital.

Ambassador Vidal was an expert in economics, trade and tariffs.He also had wide experience in multinational organizations. Before his assignment to Washington, he had headed the department of regional Latin American affairs in the Brazilian Foreign Ministry.

In the late 1950s and early 1960s, he had been a member of the Brazilian delegation to the United Nations conference in Geneva that worked out the General Agreement on Trade and Tariffs.

Later, he served as minister-counsellor of the Brazilian delegation to the Latin American Free Trade Association, which is headquartered in Montevideo, Uruguay.

Ambassador Vidal was born in Bebdeouro, Sao Paulo, Brazil. He graduated from the Pedro Segundo public school in Rio de Janeiro and then became a member of the first class to graduate from Btazil's diplomatic academy.

He began his career in Washington in the early 1950s as a third secretary in the Brazilian Embassy here. Subsequent assignments took him to La Paz, Bolivia, to Rio de Janeiro, where he worked in the department of international organizations in the Foreign national organizations in the Foreign Ministry, then to Geneva and Montevideo, and to Rome, where he was minister-councillor.

In 1970, he was assigned to Brasilia, where he headed the East European and Asian department of the Foreign Ministry before taking over the regional Latin American department with the personal rank of ambassador.

Ambassador Vidal is survived by his wife, Nair Correa de Mello Vidal, and by three sons, Paulo, 20; Fernando, 18 and Rafeal, 14, all of the resident in Washington.