Morril B. (Yank) Spaulding Jr., 64, an attorney in Washington and Maryland and owner of the Rules Service Co., a publishing firm in Bethesda, died Tuesday at Sibley Memorial Hospital. He suffered from a neurological disease.

The company, which he established 27 years ago, published legal findings and court and other rules, particularly pertaining to aviation. An aeronautical engineer as well as a lawyer, Mr. Spaulding had specialized in legal cases involving aviation.

He was born in Pittsburgh. He was a graduate of the Massachusetts Institute of Technology and the Georgetown University Law School.

Before World War II, Mr. Spaulding had represented the Glenn Martin aviation company in Africa. During the war, he was a civilian employe of the Navy Department's Bureau of Aeronautics. He also had worked for the Air Transport Association.

Mr. Spaulding practiced law until several years ago. He was a consultant to several aviation companies and was a member of the D.C. and Maryland bar associations.

He is survived by his wife, Elizabeth, of the home in Potomac: a daughter, of Washington; a son, Peter, of Frederick, Md., and two sisters, Mrs. Laurance Roberts, of Venice, Italy, and Mrs. Robert Heinemann, of Rio de Janeiro, Brazil.

The family suggests that expressions of sympathy be in the form of contributions to the Chapel Fund of St. Stephen's School in Alexandria.