Frederick D. Sisler, 63, a leading microbiologist and inventor of the prototype of the biochemical fuel cell, a method of developing cheap, long-term power sources, died of cardiac arrest Sunday at a hospital in St. Augustine, Fla. He was on vacation when he was stricken.

Dr. Sisler developed the biochemical fuel cell principle, a process that uses bacterial action to extract electric power from organic waste. He made the discovery in 1961, in his laboratory at the National Institutes of Health, by dunking two electrodes into two small test tubes, producing a one-half volt of current.One tube contained sea water, organic matter (simple sugar) and bacteria; the other contained sea water and oxygen.

The resulting energy generated by the bacterial "burning" of the organic matter was released as electricity instead of heat. [In the natural process, this energy is dissipated in heat, but Dr. Sisler obtained electricity instead of heat by having the oxygen in a separator tube.]

In a practical application of the concept being used in a pilot project in South Africa, an electrode is implanted in the sediment (mud) at the bottom of ponds of acidic water. In a typical pond, the electrons produced are tapped off and transferred from the sediment through insulated wire or another electrode at the surface of the pond.

This not only neutralizes the water but also provides electrical energy at a very low cost.

This method can be used as a means of recovering water polluted by acid water runoff from coal mines, as well as water polluted by "acid rain" fallout and other processes. In theory, it could be used to generate electricity on an isolated farm, for instance, by using septic-tank water.

Dr. Sisler retired last year from the U.S. Geological Survey, but continued as a consultant and lecturer there.

His 25 years as a government scientist included service during World War II as a captain in the Army Chemical Warfare Service and later three years as a scientist for the Central Intelligence Agency.

From 1966 to 1970, he was staff assistant to the deputy secretary for water pollution control for the Deparment of the Interior. His projects included research on the origin of petroleum for the Scripps Institution of Oceanography at the University of California at San Diego and research for the geological survey on the origin of organic matter in meteorites.

A native Washingtonian, Dr. Sisler graduated from old Central High School here. He earned a bachelor's degree in microbiology and chemistry and a master's degree in entomology from the University of Maryland. He earned a doctorate in oceanography and microbiology from the University of California at San Diego and did postgraduate work at George Washington University medical school.

He was the author or coauthor of dozens of scientific papers and held patents on an automatic fuel connector for outboard motors, and with Frank E. Senftle, on the bioelectric neutralization of acid waters, as well as the patent for the biochemical fuel cell.

His articles have appeared in such publications as Science and New Scientist magazines.

A teacher and lecturer, he participated in major scientific seminars throughout the world during his career. He lived in Bethesda.

Survivors include his wife, Mary C., of Bethesda; a son, Frederick D. Jr., of Arlington; two daughters, Rosemary Wadden of San Francisco, and Carolyn Worsley of Bakerton, W.Va.; a sister, Mildred Trisko of Crofton; and two granddaughters.

The family suggests that expressions of sympathy be in the form of contributions to the American Heart Association.