Clifton R. Wharton, the first black American career diplomat to attain the ranks of Minister and Ambassador in the United States Foreign Service, died on Monday at the Sunridge Care Center in Phoenix, Ariz. He was 90 years old and lived in Phoenix.

Mr. Wharton spent more than 40 years in the Foreign Service, capping his career with postings as Minister to Romania in 1958 and Ambassador to Norway in 1961.

Upon his retirement in 1964, he was cited by Secretary of State Dean Rusk.

''Yours has been an outstanding career, and I am sure you take pride in the fine reputation you have earned,'' Mr. Rusk wrote in a letter to the Ambassador.

Clifton Reginald Wharton was born on May 11, 1899, in Baltimore, and graduated from English High School in Boston. He earned bachelor of law and master of law degrees from Boston University School of Law, the latter in 1923.

He then joined the State Department as a law clerk and in 1924, following the formation of a career Foreign Service, became the first black to pass both the written and oral examinations and was assigned as third secretary of at the United States Embassy in Monrovia, Liberia. From 1930 to 1942 he was a consul in Las Palmas in the Canary Islands and was then named consul in Tananarive, Madagascar. He also served in Ponta Delgada in the Azores.

His first break from the traditional pattern of assigning blacks to posts in small, tropical countries came in 1949, when he was assigned as first secretary and consul in Lisbon. The following year he was named consul general and three years later was appointed consul general in Marseille, France. He remained there until 1957.

In 1958 he became the first black American career diplomat to be named of chief of a diplomatic mission when President Dwight D. Eisenhower named him minister to Romania. He was promoted to the Foreign Service rank of Career Minister in 1959. Mr. Wharton headed the mission in Bucharest until his appointment as Ambassador to Norway in March 1961.

He is survived by three sons, Clifton Jr. of Manhattan and Cooperstown, N.Y., former Chancellor of the State University of New York; William of Washington, and Richard of Hartford, Conn.; a daughter, H. Mary Sampson of Montclair, N.J.; and eight grandchildren.