Harold F. Linder, 80, a former assistant secretary of state, president and chairman of the Export-Import Bank and ambassador to Canada, died Monday at Lenox Hill Hospital in New York City following a heart attack.

Mr. Linder's first career was as an investment banker in New York. His second was with the federal government -- in addition to his work with the State Department and heading the Ex-Im Bank, he was a Navy officer stationed in Washington during World War II. His third career consisted of his work helping to resettle Jews fleeing from Germany before and after the war and with the Institute for Advanced Study at Princeton, N.J., of which he was a former chairman of the board.

A native of Brooklyn, Mr. Linder attended Columbia University and then went to Wall Street to seek his fortune. In 1933, he was made a partner in the investment banking house of Carl M. Loeb, Rhoades & Company, a position he held until 1938.

For the next three years, he devoted much of his time to the Joint Distribution Committee, an organization which assisted Jewish refugees from Nazi Germany. He served in the Navy from 1941 to 1945, rising to the rank of commander. He then returned to the Joint Distribution Committee.

From 1948 to 1951, Mr. Linder was president of the General American Investors Company Inc. in New York.

In 1951 to 1953, he was in Washington again, initially as deputy assistant secretary and then as assistant secretary of state for economic affairs.

For the next several years, he attended to his investments, served on the boards of a number of corporations and worked for the Institute for Advanced Study.

In 1961, Mr. Linder was appointed president and chairman of the Export-Import Bank by President Kennedy. He held that post until 1968, when he was appointed ambassador to Canada. He resigned in 1969.He maintained his principal residence in Washington from 1961 until 1975, when he returned to New York City.

Mr. Linder was chairman of the board of the Institute for Advanced Studies from 1969 to 1972. A professorship in the social sciences recently was established at the institute in his name.

Mr. Linder was a member of the Council on Foreign Relations, the Finance Committee of the Smithsonian Institution, the Cosmos Club in Washington and the Century Association in New York.

His wife, Bertha Linder, died in 1975.

Survivors include two children, Prudence Steiner of Cambridge, Mass., and Susan Linder of New York City; his mother, May Linder of New York City, and two grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to a charity of one's choice.