Alexander Richter, 73, an architect and builder and a professor of architecture at Howard University for 25 years, died Wednesday at Sibley Memorial Hospital. He had suffered from lung and heart ailments.

Mr. Richter was born in New York and studied at Cooper Union and the Beaux Arts Atelier there. After helping design "green belts" around Cincinnati and Milwaukee, he moved to this area in 1939, and helped plan Greenbelt, Md.

During World War II, Mr. Richter worked at the War Production Board. He later designed the town of Atentuique in the state of Jalisco, Mexico, the site of a paper mill.

But most of his work was in Washington area. He founded the Solar Construction Co., which build a number of houses in Garrett Park, and designed constructed homes in other Washington suburbs.

He was a professor of architecture at Howard University for 25 years until his retirement in 1972. He was a member of the American Institue of Architects.

Survivors included his wife, Virginia B., of the home in Garett Park; three sons, Thomas of Washington Park, N.C., Eric, of Seattle, Wash., and Mark, of Washington; a sister, Edna Shapiro, of Palm Beach, Fla., and two grandchildren.