The extraordinary show the D.C. Youth Ensemble has gotten together under the heading ''Minstrelsy: Days Long Gone By'' is an object lesson in applied history. The saying goes, if we don't learn from mistakes of the past, we'll learn from mistakes of the past, we'll be condemned to repeat them. Carol Foster, director of DCYE, and Pamela Alexander, its musical director, have chosen to exhume a particularly sensitive slice of our cultural past, the more fully to savor the present and future. And they've done so in a highly entertaining, as well as instructive, manner.

The minstrel show of the 19th century is a painful topic for both blakcs and whites: for whites because it epitomizes the denigration and repression their long march toward social justice had to contend with. But to ignore minstrelsy is to overlook an enormously rich strain of black creativity, and that is the point of the DCYE show -- as Foster puts it in a program note, ''to restate the strong influence Afro-American culture has had and continues to have on performing arts in America.''

The show as staged last nght at St. Martin's Church in the Bloomingdale community represents a second phase in a ''work in progress' that its creators intend to refine still further. An earlier version was shown last March at the downtown YWCA to much acclaim. Among the additions last night was a prefatory parade -- a staple of the historic minstrel show -- that wended its way some 15 blocks through the neighborhood, complete with horse-drawn surrey, a 935 Rolls Royce, a marching band and the two dozen performers of the DCYE in full minstrel regalia.

The show itself follows the outlines of the traditional minstrel show, but it's framed within the context of historical commentary, delivered by a lively DCYE pair. The performance needs some pruning and sharpening, but the verve and talent of the cast make this unusual production a stunner all same -- Foster and the DCYE ought to be declared a municipal treasure. An encore performance takes place Saturday; the parade starts at 2 p.m., the performance at 3, in Union Temple Church, 2002 14th St. SE.