Ernest F. Mechlin Jr., 65, a retired stockbroker who had worked as a metal specialist for the old Office of Emergency Management and later headed the Washington office of the Crucible Steel Co., died of a heart attack Monday at his home in Palm Beach, Fla.

A native of Washigton and former resident here, he moved to Palm Beach after retiring in 1973 as a stockbroker with Paine Webber.

Mr. Mechlin graduated from Western High School and Dartmouth College. He worked for the Georgetown branch of Riggs National Bank and then served as a captain in the Army Ordnance Corps in Europe in World War II.

After the war, he worked as a mental specialist for the Office of Emergency Management. From the mid-1950s until 1962, he was a vice president of Crucible Steel and headed the company's Washington office.

Mr. Mechlin then worked as a stockbroker for Johnston Lemon and Co. Inc. here until 1970, when he joined Paine Webber.

He was a member of the Chevy Chase Club and the Army & Navy Club in Washington and was a past commander of the Augustus P. Gardner Post of the American Legion.

His wife, the former Georgiana Kimball, died in 1974.

Survivors include three daughters, Diane Driscoll of Gaithersburg, Deborah A., of Boston, and Georgia A., of Frederick, Md.; two sons, Ernest F. III, also of Frederick, and Thomas K., of Palm Beach; a sister, Margaret Presley of Charlotte, N.C., and a brother, Wilmer, of Chevy Chase.

The family suggests that expressions of sympathy be in the form of contributions to the American Heart Association, or to Christ Episcopal Church, Washington.