Jack W. Dixon. 73, who served as a special consultant to the United Nations and who was active in Arlington civic and community affairs, died of congestive heart failure Monday at Northern Virginia Doctors Hospital.

Mr. Dixon, a hydraulic engineer and an expert on water rights, had maintained a home in Arlington since 1940.

In 1954, he moved to Chicago to join the Harza Engineering Co. While with the company, he also worked as a consultant to the U.N. on water resource projects in the Middle East, South America and elsewhere.

A native of Burlington, Iowa, he earned an engineering degree at the University of Iowa.

Mr. Dixon began his career in government as a civilian employe with the Army Corps of Engineers. When he returned here from Chicago about 1962, he worked for the Department of Commerce until his retirement in 1970.

He then became an engineering consultant. He also was active in civic affairs and representated the Old Dominion Citizens Association at Arlington County Board meetings.

He was a member of the Mount Vernon Yacht Club. His professional memberships included the American Society of Civil Engineers, the American Geophysical Union and the International Water Resources Association.

Survivors include his wife. Katharine, of the home in Arlington; two daughters, Eleanor, also of Arlington, and Anne Laking, of Arnold, Md.; a sister, Edith Leopold, of Burlington, and four grandchildren. CAPTION: Picture, Jack W. Dixon