W. Ray Smith, 77, a retired government civil engineer who helped plan the extension of the east front of the Capitol and the construction of the Rayburn House Office Building, died of cancer Thursday at Arlington Hospital.

Mr. Smith also worked on several projects in private industry here and laid out the first industry in the Shirley Duke garden apartment complex in Alexandria.

He was born in Farmville, N.C., and earned an engineering degree in 1924 from North Carolina State University. He then worked as a resident engineer for the city of Wilson, N.C., as an employee of the Tennessee Highway Department, and was a member of a surveying party that did the first precision mapping of the Eastern Seaboard for the U.S. Coast and Geodetic Survey.

Mr. Smith also helped survey and build Army facilities at Ft. Bragg, N.C., in 1941 and 1942, and spent nine years working as a consulting engineer on roads, dams and other municipal projects in several North Carolina cities.

From 1944 until his retirement in 1968, he was an estimator and contract analyst for the General Services Administration and the Navy Department. He helped plan construction of the main administration building at the National Institutes of Health and expansion of Smithsonian Institution facilities.

He remain active after retirement as an engineering and surveying contractor.

Mr. Smith helped found the Fair Park Baptist Church in Alexandria, of which he was a charter member. He also served as chairman of its board of deacons. He was a master Mason.

Survivors include his wife, Ellen, of the home in Alexandria: two sons, Dr. Kendall O. Smith, of San Antonio, Tex., and Donald Smith of Washington, two sisters, Delma, of Vass, N.C., and Nola, of Farmville, N.C., and threegrandchildren.