Clinton Everett Knox, 72, former U.S. ambassador to Haiti who was held hostage by Haitian terrorists in 1973, dies of cardiac arrest Thursday at his Silver Spring home.

A career Foreign Service officer, Dr. Knox served as U.S. ambassador to Haiti from 1969 until his retirement in 1973, shortly after Haitian gunnmen demanding the release of political prisoners held him and the American consul hostage for 23 hours. The diplomats were released unharmed after the Haitian government agreed to pay $70,000 in ransom and to fly the terrorists and 12 political prisoners to Mexico.

Dr. Knox entered the State Department in 1945 after earning a doctorate in history at Harvard University and teaching at Morgan State College. He began his career as a research analyst and later served as chief of the northern and western European branch of the division of research for Europe.

He was a political officer at the NATO Defense College in Paris, counselor of embassy and deputy chief of mission and consul in Honduras and U.S. ambassador to the West African Republic of Dahomey, now Benin, before becoming ambassador to Haiti. In 1966, he received the State Department's Superior Honor Award.

Dr. Knox was born in New Bedford, Mass. He earned a bachelor's degree in history from Williams College and a master's degree in history from Brown University. He was a member of Phi Beta Kappa and DACOR, an organization of retired diplomatic and consular officers.

Survivors include his wife, the former Clementine Murphy, of Silver Spring; a daughter, Karen, and a son, William E., both of Philadelphia; a brother, Dr. William J. Knox of Rochester, N.Y., and a sister, Alberta K. Eatmon of Burlington, N.J.

The family suggests that expressions of sympathy be in the form of contributions to the DACOR Scholarship Fund, 1818 H St. NW.