Gerard V. Hemelt, 80, a retired security agent in the State Department whose duties included accompanying foreign dignitaries on trips in the United States, died Thursday at the Chevy Chase Nursing and Convalescent Center in Silver Spring following a heart attack.

Mr. Hemelt, a native of Baltimore, began his government career in 1971 in the old Post Office Department, where he became a postal inspector. He served in the Army during World War I and then returned to the Post Office.

In 1940, he transferred to State as a special agent in the security division. He headed the Philadelphia office from 1942 to 1946 and also was in charge of security in Washington and New York. He established field offices in Miami and Denver.

One of his duties was to arrange security for visiting dignitaries. Among those he accompanied on travels in this country were Sir Winston Churchill, the Duke and Duchess of Windsor, Emperor Haile Selassie of Ethiopia and former King Peter of Yugoslavia.

At the time of his retirement in 1958, he was inspector general of domestic field operations in the State Department's security division.

After leaving the government, Mr. Hemelt worked for three years for the National Association of Retired Federal Employees.

He lived in Baltimore until joining the State Department. He then moved to Silver Spring, where he was a member of St. Michael's Catholic Church.

He also was a 4th-degree member of the Rosenteel Council No. 2169 of the Knights of Columbus and a member of the Alcantara Caravan of the International Order of the Alhambra.

Survivors include his wife, Gladys K., of Silver Spring; two children, Gerard A., of Lanham, and Dolores Latchford of Glen Burnie; and seven grandchildren.