WE'RE REALLY in the process," says Donald McKayle. "Come on opening night and then come again a couple of weeks later, and you're likely to see two quite different shows."

McKayle is the guiding creative spirit -- originator, director and choreographer -- for "Sophisticated Ladies," which opens a four-week run Tuesday at the Kennedy Center Opera House, and he has a kind of problem show people dream about: more good material than he can use. The show is based on the music of Duke Ellington; at this point in the process it uses 45 of his compositions in whole or in part -- not counting some melodies used in the overture. That is down from the 50 numbers it had when it began trying out in Philadelphia, and it is only about one-twentieth of the material McKayle examined when he was preparing the show.

"I came into it a year ago last October," McKayle recalls, "after the producers had secured the stage rights to the music. As soon as I was given this as a project, I jumped into everything I could get my hands on, including about 900 pieces of music -- sheet music, records, tapes, interviews. iThere are a lot of Duke Ellington fans who suppled me information and taped conversations, and Mercer Ellington had all kinds of material.

"My problem was what to do with it all. How to take all the main musical moments of his life and transform them into a theatrical presentation. How to make jazz work in the theater; they do not usually go hand in glove, you know. What type of talent to use. How to make a stage presentation of the orchestra, which was the Duke's instrument.

"I'm still working on these questions and will be until the show reaches New York. Once an idea becomes a fact, up on the stage, you see what works and what needs to be changed."

One thing that should work is the show's basic ingredient: Ellington's music, which will be played by a 20-piece band under the direction of the composer's son, Mercer Ellington. The band will include six soloists who are traveling with the show, and it will use Ellington's original arrangements -- an important point because Duke Ellington was one of the most precise orchestrators the 20th century has produced. His music often seems to be conceived as much in terms of the instrument as the motifs -- perhaps even of the instrument as played by a particular person. The show takes full advantage of this asset. "It's wall-to-walllar person. The show takes full advantage of this asset. "It's wall-to-wall music." says McKayle.

"There is so much material," McKayle says, "and there is a very definite Ellington signature on all of it, although it was written over a long period of time and in many different forms."

McKayle worked with Ellington on a couple of television shows ("A Drum Is a Woman") and ("Strolling '20s") and was beginning to work with him on a new project just before his death in 1974. "It was an unfinished opera, 'Queenie Pie,' about an aging opera singer who is challenged by a younger singer," he recalls. "It was a fantasy -- so beautiful -- and it was going to be done on National Educational Television. We had some production meetings, and the Duke was to be narrator, but he went into the hospital and then he died. There's a lot of material, but the Duke never got around to organizing it; he just kept on producing more material until the end. He was always moving ahead and wouldn't look back. Someone might be able to work it into a form that could be produced."

There are five producers for "Sophisticated Ladies," and idea that was born about five years ago, more or less simultaneously in several minds. Louise Westergaard and Sondra Gilman were partners already when they began trying to obtain rights to Ellington's music for a stage production, and Manheim Fox was working independently on the same idea. "They found out about each other's projects because they were both going to the same people," says McKayle, "and they decided to make it a joint project." The other two producers are Burton Litwin, vice president of Belwin-Mills, one of the principal publishers of Ellington's music and a company involved in a number of Broadway musicals, and Roger Berlind, who has previously been involved in productions that range from the Richard Rodgers musical, "Rex," to Peter Shaffer's "Amadeus." It took them about three years to secure the rights to Ellington's music from all the various companies that have published him.

"We have tried to use examples o all the different kinds of music Duke Ellington composed," says McKayle: his ballet music, his sacred music, all of his major pop tunes and such jazz classics as 'Cotton Tail,' 'Caravan,' 'Coco' and 'Take the A Train.' When I was going through the material, I was constantly amazed at the music, the hormonies, the orchestration. I don't know how he could have been writing some of these pieces as pop music in the '30s and '40s."

The show does not go into Duke Ellington's biography in any detail, McKayle said, "It tries to show the world he lived in as expressed through his music; the sources of his inspiration -- particularly women -- and the way he worked. Its unifying motif is the music and the various parts of life it touches."