Eugene B. Casey, 82, a multimillionaire Washington area builder and investor who became one of the largest landowners in Upper Montgomery County during the years after World War II, died of cardiopulmonary arrest July 29 at his home in Potomac.

Mr. Casey was also a former aide to President Franklin D. Roosevelt. He served as director of the Farm Credit Administration in 1940 and 1941, and later as a White House agricultural adviser. He was an enthusiastic supporter of Roosevelt's New Deal during the 1930s, and at the time he called his Maryland landholdings "New Deal farms."

As an activist in Maryland's Democratic Party, Mr. Casey was influential in persuading the Maryland delegation to the 1944 Democratic National Convention to support Sen. Harry S Truman (D-Mo.) over the incumbent, Henry A. Wallace, for the vice presidential nomination. Earlier, he had directed Roosevelt's unsuccessful efforts to unseat Sen. Millard D. Tydings (D-Md.) in 1938.

In 1946, Mr. Casey was indicted on charges of evading $70,000 in federal income taxes during the years 1941 through 1943. He had worked at the White House during those years. He pleaded no contest in 1947 and served five months of a six-month sentence at the federal reformatory in Petersburg, Va.

He said that he had made "mistakes not of intent or fraud," and that his income had been underreported "because my affairs were in the hands of others." He was pardoned by President Truman in 1951.

During the trial of former Maryland governor Marvin Mandel on political corruption charges during the late 1970s, Mr. Casey figured in news accounts as the self-described front man for a group of Mandel's friends who had purchased the old Marlboro Race Track on Dec. 31, 1971.

Following the acquisition of the track by his friends, Mandel allowed the General Assembly to override his veto of legislation increasing the number of the track's racing days from 18 to 36, thereby increasing its value substantially. Mr. Casey was president of the track during 1972 and played an active part in its management. He was never charged with any wrongdoing in the case.

He was a director and the largest single stockholder in the Washington-based Financial General Bankshares Inc., a bank holding company that was sold to a group of Middle Eastern investors in the early 1980s for a profit of several million dollars to each of the major shareholders.

A native Washingtonian, Mr. Casey was a graduate of the old Central High School, and he studied mechanical engineering at Pennsylvania State University and law at Georgetown University. While still at Georgetown, he formed Casey Engineering Co., which worked on such projects as the old YWCA building in Washington, the Georgetown University Medical School, Walter Reed Army Hospital and the Madeira School in Greenway, Va. He served in the Navy in the Pacific late in World War II.

Even before the war, Mr. Casey had expanded his interests from engineering into real estate and farming, and by the mid-1940s had accumulated a fortune estimated at $2.5 million, which included six farms in Montgomery County. The postwar years were a time of dramatic and substantial increases in population and land values in Montgomery County and Washington's other suburbs, and Mr. Casey was one of several area investors who made fortunes in land dealings during that period.

He had substantial holdings in the Rockville-Gaithersburg area, where he built low-cost houses during the 1950s and 1960s, and he was one of the first to build large apartment projects in Montgomery County.

Mr. Casey was also a history enthusiast who financed the restoration of Red Hill, the last home of Virginia patriot Patrick Henry, in Brookneal, Va. He donated the Darnall Farm in Dawsonville, built in 1755, to Montgomery County. He was a benefactor of Washington College in Chestertown, Md., where the Casey Swim Center is named after him.

Survivors include his wife, Betty Brown Casey of Potomac; four daughters, Mrs. George Visnich of Coral Gables, Fla., Mrs. F.G. Kelly of Sugar Land, Tex., Mrs. David Metz of Chappaqua, N.Y., and Margaret Casey Bradd of Barto, Pa.; two sons, Eugene S. Casey of Rockville, and Douglas Casey of Washington, and 11 grandchildren.