Louis Farrakhan, the leader of the Nation of Islam, has repeated for a national television audience his description of Adolf Hitler as ''a very great man.''
Mayor Koch of New York replied in a later segment of the same program Sunday that Democrats must reject ''the racism of Farrakhan and Jesse Jackson,'' whom Mr. Farrakhan is supporting for President, if they are to win the Presidency in 1984.
Interviewed in New York on the NBC News program ''Summer Sunday U.S.A.'' by reporters at the Democratic National Convention in San Francisco, Mr. Farrakhan repeated some of his most controversial statements and challenged reporters to defend headlines such as ''Jackson Pal Hails Hitler.''
