Leo A. Diamond, 74, a lawyer who had lived in the Washington area for the past year, died Monday in Georgetown University Hospital. He had sustained multiple injuries when he was struck by a Metrobus on Dec. 30, 1979, and had been hospitalized since that time.

A spokesman for the Metropolitan police said Mr. Diamond was crossing Nebraska Avenue on Wisconsin Avenue when he stepped into the path of a bus turning onto Nebraska.

Mr. Diamond was born in New York City and reared in Gary, Ind. He earned undergraduate and law degrees at the University of Chicago, and then came to Washington in the early 1930s as a special assistant to the chief counsel of the old Bureau of Internal Revenue.

He moved to New York City in the 1940s and entered private practice. He also taught courses on tax law at New York and Rutgers universities. He was a member of the New York firm of Austin, Diamond, and Margolious, and had been a counsel to the firm since returning to Washington.

Mr. Diamond was a resident of Chevy Chase and a member of Adas Israel Congregation in Washington.

His wife, the former Dora Sniderman, died in 1975.

Survivors include a son, Joseph, of New York City; two daughters, Diane Bernstein of Washington, and Gail Schwartz of Chevy Chase; two sisters, Ethel Schechter of Chicago, and Ruth Silverman of Sarasota, Fla., and 11 grandchildren.