Fifty years after they made their debut as a team with the landmark Oklahoma!, Richard Rodgers and Oscar Hammerstein remain the preeminent musical dramatists in American theater. Others before and after them may have been wittier, jazzier, more polished, more romantic, or more sophisticated. But none have equaled the duo's ability to dramatize an individual's emotional self-discovery through the flow of words and melody. That's not to deny the material's sentimentality: Believing in humanity's innate goodness (though not naively--after all, these were Jews writing in the heat and aftermath of World War II), R & H imbued their multidimensional characters with their own strongly felt values. But those values were affirmed through struggle and hard-won growth. It takes strong singing actors to explore the elements of conflict and comedy that make the songs so much richer than is often realized. Producer Thomas Marshall, whose previous efforts have included classy concert stagings of A Little Night Music and Kiss Me, Kate, has assembled a superb quintet for this hour-long Classic American Theatre recital of songs from Oklahoma!, Carousel, South Pacific, The King and I, The Sound of Music, and Cinderella. Mary Ernster, Anne Gunn, Kingsley Leggs, Catherine Lord, and Dale Morgan have displayed exceptional acting skills as well as voices at the Chicago area's leading musical theaters, and they can be counted on to convey the complexity and humor as well as the beauty of this great material. Friday, 12:15 PM, auditorium, Harold Washington Library Center, 400 S. State; 747-4740.