Robert N. Mattingly, 93, a retired Washington educator who was principal of Cardozo High School fo r26 years, died Saturday at Howard University Hospital after a brief illness.

Born in Louisville, Ky., Mr. Mattingly attended public schools here in Washington and was graduated from the old M Street High School. At Amherst College, where he majored in mathematics and physics, he completed the normal four-year course in three with honors and was electeed to Phi Beta Kappa, the academic honor society.

Mr. Mattingly began his career in 1905 as a mathematics teacher at Armstrong High School, and the following year after a school system reorganization became head of a new mathematics department for black schools.

During the 21 yearsthat he headed the department, he also served as secretary to the board of examiners for Division II, which comprised the city's black schools, and earned a master's degree from Columbia University.

Mr. Mattingly became principal of Francis Junior High School when it was completed in 1927. One year later, he became the first principal of Cardozo High School when that school opened. The school was named for Francis L. Cardozo, principal of the high school that Mr. Mattingly himself had attended.

Mr. Mattingly's tenure at Cardozo spanned a period of rapidly growing enrollment which at times meant double and even triple shifts. He retired in 1954, the same year that the U.S. Supreme Court declared racially segregated schools to be unconstitutional.

Mr. Mattingly was a lifelong member of St. Mary's Episcopal Church where he served as a lay reader and member of the chapel committee.

Recently, Mr. Mattingly wrote and published himself several articles about the history of M Street High School - which later became in Dunbar High School - and some of its graduates who attended Amherst.

Husband of the late Mary Baltimore Mattingly, Mr. Mattingly is survived by a son, Clington, and four daughters, Ellen Brown, Anna Louise Tatum, Mary Robert Turner and Marguerite Qutoon, all of Washington, and six grandchildren.