PHILADELPHIA (AP) _ Services will be held Saturday for John B. Kelly Jr., a former Olympian and brother of the late Princess Grace of Monaco, who collapsed and died during a morning run.

Kelly, elected last month as president of the U.S. Olympic Committee, died Saturday morning at the age of 57.

Officials at the Philadelphia County Medical Examiner's Office said an autopsy was performed Saturday night, but a ruling on the cause of death would be delayed until the completion of toxicology tests in several days. Police at first blamed an apparent heart attack for the death of the former city councilman and construction official.

''I'm shocked,'' said Don Miller, former executive director of the USOC and now president of the U.S. Olympic Foundation. ''It's a loss to amateur sports in our country.

''Jack has been identified with amateur sports all his life and had looked forward with great anticipation to serving as the president of the U.S. Olympic Committee,'' Miller said. ''It's a great tragedy that this should happen before he could fulfill his dream.''

Kelly, an Olympic bronze medal winner and son of a three-time Olympic rowing champion, had served as vice president of the USOC, an organization of the 38 national governing bodies of amateur sports, from 1980-84.

''It's heartbreaking for everybody,'' said former U.S. Treasury Secretary William B. Simon, who preceeded Kelly as USOC president. He described Kelly as ''A harder worker ... someone who was willing to drop anything ... there wasn't anyone like Jack Kelly.''

Kelly's son, John B. Kelly III, said at a news conference Sunday that his father would be buried Saturday to allow many expected mourners time to reach Philadelphia from overseas. Other arrangements were incomplete.

Kelly was a scion of one of Philadelphia's most prominent families. His sister, Grace, went on to become an actress and later married the prince of Monaco.

Known since youth by the nickname ''Kel,'' Kelly was a lifelong rower, swimmer and amateur sports enthusiast. He won his Olympic bronze in the 1956 single sculls at Melbourne, Australia. He also competed in Olympic Games in 1948, 1952 and 1960. In 1947, he won the James E. Sullivan Award as the nation's outstanding amateur athlete.

Last September, he won three gold medals in the Masters Nationals, defending titles in the mixed doubles and men's eight-man crew in his age division.

Kelly for many years played the role of George Washington in the annual Christmas re-enactment of Washington's crossing of the Delaware River.

Kelly served on the City Council as a Democrat from 1968 to 1979.

A former brother-in-law, Eugene Conlan, 57, died seven hours after Kelly collapsed, also on a Center City street, but police ruled out any connection between the deaths.

In December 1982, Kelly was shot in the groin after he refused to give his wallet to a gunman in Fort Lauderdale, Fla. He recovered fully.

Kelly recently relinquished control of the family construction firm, saying family and tax considerations, combined with the time needed for his new role with the USOC, led to the move. He also was part-owner of the Philadelphia Athletic Club.

Kelly is survived by his wife of 31/2 years, the former Sandra Lee Worley; six children by a previous marriage, which ended in divorce in 1980; his mother, Margaret; and one sister.

His body was found at 18th and Callowhill streets shortly before 9:30 a.m. Saturday. Friends later said he had been jogging to the athletic club after an early-morning row. He was taken to Hahnemann Hospital at 10:30 a.m., where he was pronounced dead.

Lt. James Cahill of the homicide department said Kelly carried no identification, delaying positive identification of the body.

Conlan's body was found at 17th Street and John F. Kennedy Boulevard, just six blocks away, at 4:30 p.m., police said.

Robert H. Helmick of Des Moines, Iowa, the USOC first vice president, will service as interim president until the committee's executive board is convened to select a successor, said a spokesman for the organization's offices in Colorado Springs, Colo. Spokesman Robert Paul Jr. said no date has been set for the board meeting.