Another black-white split in the Mississippi Democratic Party was threatened today after a white chairman, backed by Gov. William Winter, was named to head the party, unseating black Democratic cochairman Aaron Henry.

Henry, along with other blacks, angrily stalked out of the meeting of the State Democratic Executive Committee, charging that Winter's support of a white chairman was "an affront to the total black community."

Blacks, in the meantime, declined to accept any party offices or participate in any votes within the 100-member Executive Committee after Danny Cupit, a white 35-year-old Jackson attorney, was elected chairman.

Cupit, who was cochairman of President Carter's campaign in Mississippi in 1976, was backed by the governor to head the party in a move that Winter said would strengthen Democratic chances of carrying the state for Carter in November.

A longtime split in the Mississippi Democratic Party between predominantly black loyalists and predominantly white regulars had been healed in 1976 when the groups merged before the last Democratic National Convention. Since 1976, the party has had black and white cochairmen and joint offices in other positions.

The party voted two years ago to adopt a constitution calling for abandonment of the cochairmen idea in 1980, but blacks recently have tried to block its implementation after Winter said he favored a white holding the chairmanship.

Henry said he and other blacks were infuriated by Winter's remarks to the State Executive Committee today recommending a white to fill the post of chairman to broaden the party base to bring in more whites.

"We thought we had gone beyond this point," said Henry, "but we've apparently lapsed back to a purely black-white situation."