John E. "Jack" McHale Jr., 78, who served four years as chief of police in Prince George's County after a 27-year career with the FBI, died Aug. 2 of congestive heart failure and liver disease at his home in Suitland.

He spent more than 30 years in law enforcement, and in a varied career Mr. McHale was also a journalist, historian and advocate for the reputation of Samuel A. Mudd, convicted of conspiring in the assassination of Abraham Lincoln. After helping direct the FBI's war on organized crime in the 1960s and '70s, Mr. McHale led the Prince George's police from 1979 to 1983. He took over the 900-member department soon after it had been accused in a Washington Post series of operating a racially biased "death squad" in the 1960s.

During his tenure, he worked to reduce racial tension in the department, promoted women, devised programs to curb drunken driving, inaugurated a new communications facility and instituted psychological support services for officers. But nothing brought Mr. McHale more attention than his statement in 1980 that marijuana should be made legal. He was the first police chief in the country to take such a stand, arguing that the fight against marijuana was as futile as the prohibition of alcohol had been in the 1920s.

"We tried to outlaw booze, and it didn't work," he told The Washington Post, adding that many crimes could be eliminated if marijuana were not so costly.

"If you legalized it," he said, "and you could buy a pack of marijuanas for what you could buy a pack of Lucky Strikes, maybe you wouldn't have so much street crime."

In any case, he said, alcohol caused far more problems for the police than did marijuana.

Other than support from the American Civil Liberties Union and the National Organization for the Reform of Marijuana Laws, Mr. McHale faced a fierce storm of criticism from political leaders and his own police force.

"It must have been a temporary lapse of sanity," said County Executive Lawrence J. Hogan Sr., who had appointed Mr. McHale police chief.

"The calls started coming in," Mr. McHale said, "saying things like: 'Marijuana is evil, and we got to keep it out of the schools.'

"I said, 'Lady, I agree with you. I'm just saying if it's legalized, the world's not going to end.' "

He emphasized that he had never tried marijuana himself.

Mr. McHale was born in Houston and served in the Navy during World War II. After editing the newspaper at a naval air base in Texas, he studied journalism at the University of Notre Dame, graduating in 1950.

He spent a year as a reporter at the Houston Press before joining the FBI in 1951. He worked in Los Angeles and San Francisco, then was assigned to the bureau's headquarters in Washington in 1958. He became chief of the Organized Crime Intelligence Unit and helped lead a three-year investigation of waterfront unions in New York. As a result, Anthony M. Scotto, a leader of the International Longshoremen's Association, was convicted of labor racketeering in 1979.

Mr. McHale also directed the FBI's investigation of the disappearance of Teamsters leader Jimmy Hoffa in 1975.

From 1970 to 1976, Mr. McHale was on the faculty of the FBI Academy, a law enforcement training center in Quantico. He lectured on organized crime at colleges and at military and law enforcement institutions.

In 1978, he accepted Hogan's invitation to work as a public safety liaison and press secretary in Prince George's. He was named acting police chief in December 1979 after the first choice for the job was rejected by the County Council, and he assumed full duties two months later. He was replaced by Michael J. Flaherty in September 1983.

In his later years, Mr. McHale turned to writing. In 1994, he published "Dr. Samuel A. Mudd and the Lincoln Assassination," a historical account defending the physician who had treated the broken leg of John Wilkes Booth, who was injured while leaping to the stage of Ford's Theatre moments after shooting President Abraham Lincoln. Mudd was the great-grandfather of Mr. McHale's wife.

Mr. McHale appeared on the "Today" show and other television programs, taking up the cause of Mudd, who served four years in prison for conspiracy until his sentence was commuted by President Andrew Johnson in 1869. Mr. McHale had a leading role in trying to clear Mudd's name in the courts, but the case was dismissed by a federal judge in 2002.

Mr. McHale was on the board of the Dr. Samuel A. Mudd House in Charles County and a member of the Surratt Society, a volunteer group devoted to preserving the Surratt House in Clinton, which was part of Booth's escape route after the assassination.

At the time of his death, Mr. McHale was completing "The FBI vs. the Mafia," a book about organized crime.

For 46 years, he was a member of St. Philip the Apostle Catholic Church in Camp Springs, where he taught religion classes for teenagers. He also coached children's softball teams.

Survivors include his wife of 53 years, Mary M. McHale of Suitland; eight children, Kathleen Shearer of West Chester, Ohio, Michael J. McHale of El Paso, Therese Gallegos of Brownsville, Tex., John E. McHale of Ellicott City, Brian K. McHale of Tehachapi, Calif., Elaine Seidman of Crownsville, Sheila Mudd of Laurel and Robin Murphy of Washington; 15 grandchildren; and a great-grandson.

John E. "Jack" McHale Jr. worked to reduce racial tension on the force.