Keith Edward Mazzi, 20, a 1979 graduate of Walt Whitman High School who was a resident of Gaithersburg where he owned and operated his own landscaping business for the past two years, died Thursday in Suburban Hospital of injuries he had received in an automobile accident the day before.

Montgomery County police said that Mr. Mazzi was driving south on Persimmon Tree Road, when at the intersection with Persimmon Tree Lane in Potomac, he was struck by a west-bound vehicle driven by Elinor Fonoroff, 65, of Silver Spring. Police said the accident happened about 1 p.m.

Police said Mr. Mazzi's vehicle overturned and he was thrown to the ground. He was taken to Suburban Hospital where he died the following day. Fonoroff was treated at the scene of the accident and later charged with failure to yield the right of way, police said. Police said there were no passengers in either vehicle.

Mr. Mazzi was born in Bethesda. He had owned and operated Mazzi Landscaping in Gaithersburg since 1979. An outdoorsman, his hobbies included camping, hunting, and fishing. He was a member of the Lakewood Country Club and had won golf trophies. He also was a member of the Pinstripe Bowling League in Shady Grove and won awards in that sport.

He was a member of the Cabin John United Methodist Church.

Survivors include his wife, Rebecca J. Mazzi, whom he married on March 22, 1980, of Gaithersburg; his father, James E. Mazzi of Glenwood, Md.; his mother and stepfather, Diane M. and Doug Earp, both of Cabin John; a sister, Deborah L. Mazzi, and a stepsister, Army M. Earp, both of Cabin John, and his grandmothers, Brace O. Mazzi and Ada Lowe, both of Cabin John.

The family suggest that expressions of sympathy be in form of blood donations in his name to Suburban Hospital in Bethesda or contributions to the American Heart Association.