Abby Watkins Bernon, 31, an artist and designer who was associated with the Smithsonian Institution as design assistant to the office of folklife, died Friday at the Washington Hospital Center of injuries sustained in an automobile accident on Thursday.

A freelance graphic artist and designer for the past two years, Mrs. Bernon recently rejoined the Smithsonian to work on designs for the Institution's Festival of American Folklife scheduled to open in October.

She previously worked for several years for the Smithsonian's division of performing arts, collaborating on the interior design of the Native American Learning Center, which was a focal point of the Smithsonian's 1976 Bicentennial Festival on the Mall.

Mrs. Bernon was injured Thursday while returning from a trip to the Smithsonian's North Capitol Street warehouse. The car in which she was riding hit a truck on the Southwest Freeway's South Capitol Street Ramp.

A native of Long Island, N.Y., she graduated from Skidmore College and moved to this area in 1970 to complete work on a master of fine arts degree, which she earned from George Washington University.

Mrs. Bernon, who was married June 7 to Douglas Bernon, a public affairs officer at the U.S. Metric Board, also had worked as a designer for the Government Printing Office for several years.

Her freelance work included displays for the National Park Service and other government agencies, as well as for private Washington area consulting and design firms.

Mrs. Bernon, who lived in Arlington, was a horsewoman and a pianist.

Besides her husband, of Arlington, survivors include her mother, Mrs. Robert Crooker of Cold Spring Harbor, N.Y.; her father, John B. Watkins of Washington, Conn.; three brothers, John L. and Charles H. Watkins, both of Washington, D.C., and David J. Watkins of London, and a half-brother, Robert Crooker Jr., of Long Island.

The family suggests that expressions of sympathy be in the form of contributions to the National Center for Therapeutic Riding, Rock Creek Park Horse Centre in Washington.