ATLANTA (AP) _ Former Secretary of State Dean Rusk is responding well to treatment for an infection that has kept him in the hospital since Dec. 26, his physician said.

Rusk, 78, who served under presidents John F. Kennedy and Lyndon B. Johnson, is recuperating at Emory University Hospital from an infection that may be related to his heart disease, Dr. J. Willis Hurst, the hospital's chief of cardiology, said in a statement Wednesday.

''Though Mr. Rusk has a number of problems, including heart disease, he was admitted for an infection that we believe is under control and he's doing well,'' Hurst said. ''He will be here for an undetermined period of time in order to observe the results of treatment.

''Mr. Rusk is alert and displays all the wisdom he's known for,'' the physician added.

Rusk is a professor of international law at the University of Georgia in Athens, where he has taught since his 1961-69 stint as secretary of state.