THE FIRST Inter-American Music Festival opens April 18 in Washington. The festival originally had been scheduled for April of last year, and New Orleans, which aspires to be the modern hub of the Americas, was the site chosen. The selection aimed to blend the old musical tradition of the city with the more recent Latin American hue that has covered the port commercially. But several months before the scheduled opening, with almost all commissioned music completed, officials mysteriously called everything off. And the music has marked time for a year. In calling off the event, the authorities concerned mumbled an odd excuse: the postponement was due to a delay in construction of an outdoor concert stage near the shores of Lake Pontchartrain. This was the first inkling most New Orleanians had that anyone ever contemplated building such a stage, and since then there has not been another scrap of information about it. Last December 8, The New York Times, while discussing the upcoming event in Washington, offered a more logical excuse: the festival was postponed last year so that it would not conflict with the program of the Institucion Jose Angel Lamas in Caracas and the Casals Festival in Puerto Rico. But this, while justifying a change of time, does not explain the change of place. Both the initial announcement and the Times interpretation were too polite to hit the mark. New Orleans did not have a music festival last year because its businessmen, who have spent quantities of money and energy in the last fifteen years to attract Latin American trade, did not feel like wasting either to attract Latin American culture. The roots of the difficulty stretch to the nineteenth century, when New Orleans was the center of French Opera in the United States...