Debar means "to shut out or exclude" (The doorman will debar all who are not members) and "to hinder or prohibit" (Debar all candidates below the age of eighteen). Disbar has much the same meanings but is applied specifically to the legal profession in the sense of "to expel": "The legal society decided to disbar both attorneys for their conduct at the trial."
Dictionary of problem words and expressions. Harry Shaw. 1975.