SHELDON HARNICK, the wordmeister for "A Wonderful Life," shares a few memories of his friend, composer Joe Raposo, who wrote the music. They worked together for 10 years on this musical that finally opened this month at Arena Stage, two years after Raposo's death.Over the years "There was a natural rapport on this musical," says Mr. Harnick. "The songs just welled out.... the feelings are very urgent in the story, and that leads very easily to songs." In spite of the fact that their temperaments were different, their work was in harmony. "Joe was wonderful, so exuberant, so optimistic all the time as opposed to pessimistic, which I tend to be," Harnick says. They met in 1965 when Harnick went to Boston to see a production of his musical "She Loves Me.Joe was the musical director.... The orchestra consisted of Joe on piano and a percussion player. I was so impressed by his the musicianship that I introduced myself at the end of the show.... and we stay ed friends." Sheldon Harnick was already the Tony Award-winning writer of "Fiorello" and "Fiddler on the Roof" when they teamed up. Raposo had come to New York and become co-creator of "Sesame Street," writing such hits as "Smile" and Kermit the Frog's aria, "It's Not Easy Being Green." They collaborated on a version of "Alice in Wonderland" by Bil Baird Marionettes, and on a short cantata for a Boston Symphony Orchestra benefit. Raposo had been a prot of composer Nadia Boulanger in Paris. When Harnick got the offer to do "A Wonderful Life," he called on Joe Raposo because "I knew that we would need both simple tunes in some places and very sophisticated mini-operas in other sections.... and I think he's done a superb job." "Although the movie is in the public domain.... the dramatic rights to the [Van Doren] story are lost," says Harnick. That delayed a major production until now. Raposo did see his musical performed once, in a 1986 University of Michigan production.