Roy Alexander, 79, a former managing editor of Time magazine, died Monday at a hospital in Roslyn, Long Island N.Y. He had broken a hip recently and had pneumonia.

Mr. Alexander spent 27 years on Time's staff before his retirement in 1966. From 1949 to 1960, he was its managing editor - the top editorial post on the publication. He held that job longer than anyone since the magazine was founded in 1923. He was executive assistant to Henry R. Luce, a founder of Time, from 1960 until his retirement.

Mr. Alexander was born in Omaha, Neb. He graduated from St. Louis (Mo.) University. He began his career in journalism with the St. Louis Star in 1921 and then switched to the St. Louis Post-Dispatch. He remained on that paper until he joined Time in 1939.

In addition to his newspaper work, Mr. Alexander was an enthusiastic pilot. He learned to fly at the Massachusetts Institute of Technology after serving in the Marine Corps in 1918 and 1919. He was an officer in the Missouri Air National Guard from 1920 to 1939. He was a part-time test pilot at the Grumman aircraft plant on Long Island during World War II.

Survivors include his wife, the former Mary Louise Webb, of the home in Sands Point, N.Y.; four daughters, Patricia LaMothe, of Battle Creek, Mich., Rosemary Alexander, of New York City, Harriet Garzero, of Port Washington, N.Y., and Hollis Nichols, of West Islip, N.Y.; three sons, Roy Jr., of Houston, Charles C., of Detroit, and Stephen W., of Chicago; 28 grandchildren, and four great-grandchildren.