Dr. Bertram Francis Schaefer, 73, a physician who practiced in Washington for more than 40 years and who was a founder of the Yater Clinic here, died Saturday at Doctor's Hospital of Prince George's County in Lanham. He had gastroenteritis.

Dr. Schaefer, who was born in Lancaster, N.Y., graduated from Canisius College in Buffalo. He then moved to Washington to attend Georgetown University Medical School, from which he graduated in 1935.

He later set up a general medical practice in Washington and continued it until 1946. In that year, he joined a group of doctors in establishing the Yater Clinic. Dr. Schaefer specialized in internal medicine. He retired in 1978.

From 1939 until he retired from his practice, Dr. Schaefer, who lived in Washington, was an associate professor of medicine at Georgetown.

He was a member of the D.C. and American medical associations.

His wife, the former Marion E. Sauter, died in 1978.

Survivors include two sons, Adrian of Largo, and Edward, of Baltimore; two sisters, Ruth and Florence Schaefer, both of Lancaster, N.Y.; two brothers, Myron, of Seminole, Fla., and Eugene, of Lancaster, and one grandchild.

The family suggests that expresiions of sympathy be in the form of contributions to the Heart Fund.