JFK, as congressman or senator, did less in favor of minorities than LBJ... JFK was a low profile politician who was aiming at the presidency and he played it safe till november 60...
During his presidency, the civil rights issue came out as an hot potatoe. A critic said of JFK that it would be better for him to show more courage and less profile... The Kennedys tried to moderate Black leaders, asked them to be more patient, but they were unable to do something concrete about that and they refuse to use LBJ's political influence to pressure the Congress...
Most of Civil Rights legislations were passed during the Johnson's Presidency, and for LBJ, Civil Rights' issue was politically a suicide... I think that, for exemple, the Housing Bill contributed more to LBJ's political downfall than Vietnam War...
-Pierre Carbonneau
P..S: I think that Earl Warren, as Chief Justice, is the character in American history who helped more to boost the Civil Rights issue with his Brown vs Board of Education judgment in 1954 and it sequels...