WILLIAMSBURG, Va. (AP) _ Carter Olin Lowance, chief of staff to six Virginia governors, has died of cancer at age 78.

Lowance, who died Thursday in a Williamsburg hospital, left the staff of The Associated Press in Richmond in 1947 to work for Gov. William M. Tuck. He served successively under Govs. John S. Battle, Thomas B. Stanley, J. Lindsay Almond, Albertis S. Harrison and Mills E. Godwin Jr.

When Republican Gov. Linwood Holton broke the long line of Democratic succession in 1970, he asked Lowance to stay on. But Lowance decided instead to take a job as executive vice president at the College of William & Mary.

''He served Virginia as well as any man I've ever known,'' Harrison said. ''Completely self-effacing, he was perfectly willing to do the work and let somebody else get the credit.''

''When Carter spoke, government listened, but he barely spoke above a whisper,'' said Gov. Gerald L. Baliles. ''While others governed, Carter guided. He was cautious, always knowledgeable and steady at the wheel.''

Survivors include his wife, Elizabeth Austin Lowance, a sister, Mrs. George Lieben of Tucson, Ariz., and a brother, Franklin Lowance of Williamsburg.

Funeral arrangements were incomplete.