Dr. Gordon V. Halahan, 56, an oral surgeon who had maintained offices in Bethesda since 1955 and who was a former president of the Southern Maryland Dental Society, died of cancer Thursday at his home in Potomac.

Dr. Halahan, who was born in Brooklyn, N.Y., served in the Navy Seabees during World War II and saw service in both the Atlantic and the Pacific. He was present on Omaha Beach on D-Day during the Normandy invasion.

He moved to Washington after the war to become a student at Georgetown University. He earned his dental degree in 1952 under an accelerated program available to veterans, and his doctorate in oral surgery in 1955.

He then established his practice in Bethesda and continued it until his death.

In addition to his work with the Southern Maryland Dental Association, Dr. Holahan was a member of the American Society of Oral Surgeons. He also was a member of the Potomac and Middletown Valley hunt clubs and the National Ski Patrol.

Survived include his wife, Mary G., of Potomac; five sons, Gordon V. Jr., of Ann Arbor, Mich, and Edward C., Joseph T., Michael P. and Sean W., all of Potomac; three daughters, Patricia Gellatly, of Baltimore, and Maureen and Elizabeth, both of Potomac, and his mother, Mrs. E. C. Holahan, of Westhampton Beach, N.Y. Another daughter, Cathleen, died in 1966.

The family suggests that expressions of sympathy be in the form of contributions to the Vincent T. Lombardi Cancer Research Center, Georgetown University Hospital, 3800 Reservoir Rd., Washington, D.C., 20007.