Francis C. O'Donnell, 70, a former mayor of Bladensburg and a retired D.c. battalion fire chief who was cited for his bravery and credited with developing innovative firefighting methods, died Friday at Prince George's General Hospital after a heart attack.

Three months after joining the D.C. Fire Department in 1933, Mr. O'Donnell won a medal for bravery for rescuing three children and a woman from a burning house in Georgetown. Four years later, he was honored for his actions in rescuing two women from the fourth floor of a burning building by using his body as a bridge between the tip of a fire ladder and a window of the building, enabling another firefighter to pull the victims across his body to safety.

In 1948, as a sergeant in command of a fire truck company, he tore loose a fellow firefighter's hands, which were frozen to a metal ladder on top of a downtown building, and pulled him through dense smoke to safety.

Mr. O'Donnell, who studied and experimented with scientific firefighting techniques, came up with a number of innovations that were adopted here and copied throughout the nation. These include the use of compressed air masks by engine companies, methods for fog firefighting, a system for hooking two pumps together for double pressure, the use of various hoses and nozzles to get more water faster, and techniques to use the least amount of water in the most effective way.

As battalion chief, to which he was promoted in 1958, he spearheaded a committee charged with drawing up detailed "pre-plans" to deal with fires in each of several hundred city blocks where there was a major hazard or high-value property. The first such pre-plan was for the block bounded by 13th, 14th, E and F streets NW.

Mr. O'Donnell served as acting deputy fire chief before retiring from the Fire Department in 1962, because of back injuries suffered in the line of duty.

After retiring, he turned down several fire department offers, and decided to run for mayor of Bladensburg. He was elected to office in 1963 and re-elected to five more terms before retiring a second time in 1974, also for reasons of health.

His achievements as mayor included increased municipal services, an improved police department, wide-reaching street paving and lighting programs, development of two playgrounds and construction of a town office building. He received a plaque from residents and merchants of Bladensburg when he retired for his leadership in expanding and improving services and providing efficient, quality government "without increasing taxes."

A resident of Bladensburg, Mr. O'Donnell was born in Everett, Mass. His first wife, Mary E., died in 1966.

Survivors include his wife, Delia R., whom he married in 1971; a sister, Marion, of Everett, and a brother, John, of Chelsea, Mass.