Dr. Paul A. Morin, 71, an oral surgeon and specialist in cancer detection who retired from private practice in July, died Thursday at Sibley Memoral Hospital following surgery for a perforated ulcer.

Dr. Morin was chief oral surgery at Webber Hospital in Biddeford, Maine, before moving to Washington in 1951. He then established a private practice here. He also was affiliated with Providence Hospital, where he specialized in oral surgery, and the Walter Reed Army Medical Center, where he specialized in cancer detection.

He established a dental clinic at the Washington Home about two years ago.

Dr. Morin was born in Biddeford, and earned a bachelor's degree from Dartmouth College. He earned degrees in medicine and dentistry from the dental and medical schools at Tufts University in Medford, Mass.

He was a life member of the American Dental Association and the D.C. Dental Society. He also was an associate member of the D.C. Medical Society and was active in the Capital Area Boy Scouts. He was a former president of the Northeastern and Maine Dental Societies.

Dr. Morin lived in Washington and also had maintained a home in Saco, Maine, until recently.

Survivors include his wife of 41 years, the former Gertrude Potter, of Washington; two sons, Lawrence P., of Lynchburg, Va., and Paul A. Jr., of Randallstown, Md.; two brothers, John D. II, of Old Orchard Beach, Maine, and Norman G., of Biddeford, and four grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to St. David's Episcopal Church in Washington.