Has performing in blackface gone the way of gin joints and the WPA? Yes, says Keith M. Jones, president of the New Jersey State Conference of the National Assn. for the Advancement of Colored People. No, replies Bernard C. Algard, a New Jersey-based carpet salesman by day and Al Jolson impersonator in clubs by night. Jones said Tuesday he plans to launch an economic boycott against organizations that employ Algard, who maintains his act in not racist but a re-creation of an era. Jones says the show epitomizes outdated stereotypes of blacks and can only exacerbate racial tensions, but Algard says blacks attending his shows have not complained.