NEW ORLEANS voters elected a new mayor last week. He's Ernest N. (Dutch) Morial, the city's first black mayor. He will be responsible for - and to - the largest constituency of any black elected official in the South. Preferring instead to talk about the city's fiscal health, Mr. Morial didn't make much of his race during the campaign. His opponent attempted to do so in a negative way, but 51 per cent of the voting electorate agreed with Mr. Morial that "it is not blackness but executive ability that will solve the [city's] problems."

By that standard - ability and a commitment to civic progress - Mr. Morial stood out as a candidate to succeed Mayor Moon Landrieu, who had served two terms and statute could not succeed himself. A New Orleans native who was the first black graduate from the Lousiana State University Law School, Mr. Morial, 49, has had a varied career as civil-right activist, Assistant U.S. Attorney, state legislator and state appeals-court judge. This record attests to the racial progress in the South in just a decade. It says a good deal that, during the racially turbulent early 1960s, Mr. Morial was the very active president of the local NAACP.

Mr. Morial's win wasn't unexpected. Over 98 per cent of the black voting last week chose him. But so did over 20 per cent of the white voters - a figure three times greater than the white vote he received in the primary. That, we feel, is an indication of the progressive spirit abroad in New Orleans these days. Although obviously the reasons for that are numerous, few, we think, would question thta outgoing Mayor Landrieu deserves a major share of the credit. In his seven years in office, Mr. Landrieu pushed and pulled a once languishing New Orleans into the front rank of American cities. He integrated the city hall work force at all levels. He led the effort to revitalize the city'c central business district. As president of the U.S. Conference of Mayors, he vigorously championed increased federal aid to urban areas - including emergency help for beleaguered New York City. In doing so, Mayor Landrieu brought a national dimension to his office and his city. He helped create the climate in New Orleans that made Mr. Morial's election not only possible but probable.

No one assumes that New Orleans has reached the promised land either in relations between the races or in solving its other problems. But Mr. Landrieu has left a good foundation on which Mr. Morial can build.