Sir Albert M. Margai, 70, who served as Sierra Leone's prime minister from 1964 to 1967, died of a heart attack Thursday at Montgomery General Hospital in Olney.

Sir Albert, who had been living in exile in London, was visiting a niece in suburban Maryland when he was stricken. As part of a private visit to this country, he had planned to tour several U.S. cities to address groups of Sierra Leonans.

Samuel G. Tucker, husband of Sir Albert's niece, said, "He was in political exile, doing nothing really, living as a private citizen in London." p

Sir Albert succeeded his brother, Sir Milton Margai, who served as the first prime minister of the West African nation from 1961 to 1964, after it had achieved independence from Great Britain. Sir Milton died in 1964.

He previously served as Sierra Leone's finance minister and as minister of natural resources.

A London-trained lawyer, he was a founder, with his late brother of the Sierra Leone Peoples' PARTY (SLPP). In 1957, after being elected party leader over his brother by a one-vote margin, he resigned the post in favor of Sir Milton. The brothers later grew apart politically. t

Sir Albert resigned from the SLPP in 1958 to form his own party, the Peoples National Party (PNP), which supporters claimed was dedicated to a more militant government policy.

He remained as opposition leader until 1960, when he agreed to bring the PNP into an all-party national front, which his brother had formed before pre-independence constitutional talks in London. After independence was granted, he joined his brother's coalition government as minister of natural resources.

At the time of his break with his brother, Sir Albert accused Sir Milton of being under too much British control.

Sir Albert left office in March 1967 after turbulent national elections sparked four successive coups within a week.

Survivors include his wife, Lady Princess Margai, and 10 children.