William Martin O'Neil, 69, an architect who owned the William M. O'Neil architectural firm in Silver Spring for 17 years until he retired in 1977, died of arteriosclerotic cardiovascular disease Jan. 20 at his home in Silver Spring.

Mr. O'Neil was born in New York City and reared in Washington. He was a graduate of St. John's College High School and earned his bachelor's degree in architecture at Catholic University in 1937. He attended the Architectural Association at the University of London. He served with the U.S. Army Corps of Engineers in Europe in World War II.

Before establishing his firm in 1960, he had worked for the architectural firms of Soule and Donnelly in Chevy Chase and Kass-Berger in Washington.

Mr. O'Neil was a member of the American Institute of Architects, the Rock Creek Watershed Association and St. Peter's Catholic Church in Olney.

Survivors include his wife, Louisa W.P. O'Neil of Silver Spring; three daughters, Louisa W.P. O'Neil of St. Petersburg, Fla., Sara P. O'Neil-Manion of Bethesda, and Rebecca M. O'Neil of Louisville, Ky.; two sons, Matthew J. H., and William M., both of Silver Spring; two brothers, John K., of Friday Harbor, Wash., and Paul T., of Bethesda; two sisters, Nora Lamborne of Sligo, Ireland, and Barbara Hogan of Washington, and a grandchild.