Life on the Mississippi, Through a Musical Lens.

While Lincoln Center presents a splendid revival of ''South Pacific,'' inviting audiences to consider the prejudices of white Americans against ''people whose skin is a different shade'' (as one of its songs puts it), Gateway Playhouse in Bellport is mounting an earlier landmark musical by the same librettist-book writer exploring the same theme. ''Show Boat,'' with book and lyrics by Oscar Hammerstein II, was groundbreaking in several ways. It integrated songs and plot into what many critics deem the first serious American musical and had black and white performers sharing the stage. [ABSTRACT FROM PUBLISHER]