Michael Kwapiszewski, 96, who served as Poland's envoy to the United States in the early 1920s and 1930s and again during World War II, died of cardiac arrest Wednesday at St. Joseph's Nursing Home in Catonsville, Md.

Mr. Kwapiszewski served as Poland's representative to this country with the rank of minister plenipotentiary and envoy extraordinary throughout World War II, resigning his post in July 1945, when the United States formally recognized Poland's communist government.

He began his diplomatic career in the early 1920s when Ignacy Jan Paderewski, the renowned pianist who served for about 10 months as prime minister of a Polish coalition government, appointed him counselor of Poland's embassy here.

Mr. Kwapiszewski subsequently served as chief of the division of the Americas and the Far East in the Polish Ministry of Foreign Affairs, as Poland's envoy to Norway, Yugoslavia and the Union of South Africa and as envoy to this country from 1932 to 1935.

After resigning from the Polish Foreign Service, he worked as a researcher for the Library of Congress for 15 years, retiring in the mid-1960s.

Born in Gorlowka in the Ukraine, Mr. Kwapiszewski attended college in Russia. He graduated from the universities of Kharkov and Warsaw and the Royal Technical College of Dresden, Germany.

A former Washington resident, he had lived at St. Joseph's Nursing Home in recent years.

Mr. Kwapiszewski's wife, Clara, died in 1978. There are no immediate survivors.

The family suggests that expressions of sympathy be in the form of contributions to the Sister Servants of Mary Immaculate at St. Joseph's Nursing Home in Catonsville.