Arnold Christen, 64, a senior partner in the patent law firm of Fisher Christen & Sabol, died of a pulmonary embolism Sunday in his home in Annapolis.

Mr. Christen had practiced law in Washington for 35 years and was an authority in chemical and pharmaceutical patents. Over the years he had chaired several committees of both the American Bar and American Patent Law associations.

He was a native of Iowa and a 1938 graduate of the University of Iowa, where he was an intercollegiate diving champion. During the 1930s, he also toured with Aquacade shows featuring Eleanor Holm and Adolph Kiefer. Mr. Christen starred in a clown diving act.

He graduated from the Georgetown University's law school and served in the Navy as a lawyer during World War II. He also put on his diving clown show for Navy personnel in hospitals and bases around the country during the war.

Mr. Christen's survivors include his wife, Hedwig G. Christen of Annapolis; a son, Lee, of Falls Church; two daughters, Carol Christen of San Francisco, and Madeleine Glennon of Annapolis; a brother, Eugene, of Birmingham, Mich.; a sister, Marie McBurney of Waldorf; and one grandchild.

The family suggests that expressions of sympathy be in the form of contributions to the Dr. Philip S. Schein Division of Medical Oncology at Georgetown University.