Walter J. Bierwagen, 75, who was the legislative director and international vice president of the 165,000-member Amalgamated Transit Union from 1963 to 1981, died of cardiac arrest April 26 at the Greenbelt Convalescent Center. He lived in New Carrollton.

Mr. Bierwagen, in a union career here that spanned 45 years, also had served as a vice president of the Virginia State AFL-CIO and the Maryland-D.C. Federation of Labor. During the 1960s, he was secretary of the Greater Washington Central Labor Council.

In the mid-1970s, he was a labor representative to the International Labor Organization in Geneva, and he served on the Presidential Commission on Aging during the Carter administration.

Mr. Bierwagen was a native of South Bend, Ind., and moved to this area in 1936. He joined the transit union local that year and drove a bus until about 1950. He was elected to the local's executive board in 1947 and also served as business manager before serving as local president from 1952 to 1963.

During his union career, he advised presidents on mass transit matters and was a leader in organized labor's role in the creation of the Washington Metropolitan Area Transit Authority and Metrorail service. He was chief negotiator for his union in the first collective bargaining agreements with Metro.

Mr. Bierwagen had served for a decade as president of the Greenbelt Consumer Services Co-op. He also had been a member of the board of the Group Health Association. He had worked on such civic matters as home rule, education and race relations.

Survivors include his wife, Freda, of New Carrollton; a son, Ronald, of Laurel; a daughter, Marilyn Tompkins of Seabrook, Md.; four grandchildren, and two great-grandchildren.