JAMES GARFIELD ELLIS JR., 71, an official of the Motor Vehicle Manufacturers Association, formerly the Automobile Manufacturers Association, for more than 30 years, died Saturday at Nantucket Island, Mass., following a heart attack.

He was stricken on a cruise ship and was pronounced dead at Nantucket Cottage Hospital.

Mr. Ellis, a resident of Rossmoor Leisure World in Silver Spring, was born in Beaver, Pa., and grew up in Jamestown, N.Y.

He moved to Washington in 1928 and worked for the government while attending night classes at George Washington University, where he earned a bachelor's degree, and Southeastern University, where he earned a law degree.

In 1937, he went to work for Chilton Publications, which publishes trade journals. He began his career with the Automobile Manufacturers Association in 1941.

From 1969 to 1972, he managed the organization's Washington office. From 1973 to 1974, when he formally retired from the association, he was executive secretary of the Council of Defense and Space Industries Associations. Mr. Ellis remained a consultant to the Motor Vehicle Manufacturers Association until his death.

He was a past president of the D.C. chapter of the Public Relations Society of America, the Chevy Chase Citizens Association and the Woodrow Wilson High School Home and School Association. He belonged to the American Society of Association Executives, the National Press Club and the Army & Navy Club. He also was a member of Metropolitan United Methodist Church.

Survivors include his wife, Marian, of the home; a son, James Garfield III, of Phoenix, Ariz.; two daughters, Marianne Alexander of Ellicott City, Md., and Kaethe Williams of Steamboat Springs, Colo.; a sister Evelyn Cole of Corpus Christi, Tex., and six grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the American Heart Association.