Joseph S. Cassells, 69, a Navy physician and rear admiral whose final active-duty position, in 1988, made him responsible for the management of the Navy's 31 hospitals and 200 medical clinics worldwide, died of pancreatic cancer July 2 at his home in Bethesda.

Adm. Cassells headed the Navy's entire medical operations and budget while serving in Washington from 1985 to 1988.

Earlier, he was medical director of the Marine Corps and a senior officer of naval medical regional clinics in San Diego and Charleston, S.C.

Born in Chester, S.C., Adm. Cassells graduated from Duke University's medical school in 1960 and received a master's degree in public health from Johns Hopkins University in 1968.

In the 1960s, he served as general medical officer of the 3rd Marine Division in Okinawa and chief of medicine at a naval hospital in Subic Bay, Philippines.

As malaria and other tropical diseases became a growing concern during the Vietnam War, Adm. Cassells obtained a fellowship from Johns Hopkins to study that type of illness.

His studies, which included a year of research in Calcutta, led to his positions as a consultant in tropical diseases and chief of the parasitology division of the Naval Medical Research Institute.

Adm. Cassells had moved into health care administration and management by the late 1970s.

His military decorations included the Legion of Merit and the Meritorious Service Medal.

After retiring from active military duty, Adm. Cassells worked at the Institute of Medicine at the National Academy of Sciences and served on the Presidential Advisory Committee on Gulf War Veterans' Illnesses.

At the Institute of Medicine, he helped direct studies on health promotion and disability prevention for older adults.

Survivors include his wife of 39 years, Judith M. Cassells of Bethesda; two children, Jennifer Cassells of Ashton and Caroline Cassells of Philadelphia; his mother, Azilee Cassells of Chester; a sister; and two grandchildren.