Norman Diamond, 85, a senior partner in the Washington law firm of Arnold & Porter where he had specialized in general litigation and antitrust and trade regulation, died of a heart ailment Nov. 9 at his home in Potomac.

Mr. Diamond joined what became Arnold & Porter, which now has 530 lawyers, in 1946. Over the years, he served as a Washington counsel for such companies as Kroger groceries, Federated Department Stores, Lever Bros., Coca-Cola and the old Washington Star newspaper.

In 1997, he published a memoir of his experiences in the early years of his law firm called "A Practice Almost Perfect."

Mr. Diamond, who was born in Brooklyn, N.Y., was a 1935 graduate of the University of North Carolina. He was a 1938 graduate of Yale University law school, where he served on the board of editors of the law review. His Yale professors included Abe Fortas, a future associate justice of the U.S. Supreme Court, and Thurman Arnold, both of whom were founders of Arnold & Porter.

In 1938 and 1939, Mr. Diamond was an assistant district attorney for New York County, where he worked under Thomas E. Dewey, a future New York governor and two-time Republican presidential candidate.

Mr. Diamond came to Washington in 1939, and was a government lawyer until 1943. During those years, he served first with the Interior Department, then as chief counsel of the solid fuels branch of the Office of Price Administration, and then as a claims division attorney in the Justice Department. From 1943 to 1946, he served in the Navy.

He was a member of Washington Hebrew Congregation and Woodmont Country Club.

Survivors include his wife of 58 years, Luna, of Potomac; two children, Monty, of New York, and Sarah Diamond of Aspen, Colo.; a brother; and a grandchild.