Reprinted from yesterday's late editions

Because jazz is basically an impo-visational form of music, much of its power is derived from the emotional expressiveness of the musicians and the way in which they interpret a given song.

Without this emotional commitment or material that accentuates that commitment jazz ceases to be jazz and becomes a milder form of pop music.

Thursday night at Wolf Trap, in a live television broadcast, Chuck Mangione was both a jazz and pop musician. Playing before a packed house (and lawn) he and his quartet and 10-piece orchestra moved from soft easy ballads to intense musical sections in which the musicians seemed completely absorbed in their music. When the set was hot it sizzled; yet when it was bland, it was the next best thing to a concert by the Tijuana Brass.

The main reason for the unevenness of the show was Mangione's compositions. He favors long, extended phrases and thick, lush harmonies. On songs like "Land of Make Believe" and "The 11th Commandment" this approach was effective. However, many of the other pieces resembled nothing more than the background music for a romantic television series.

The songs were saved at times, by the imagination and technical proficiency of the musicians.Mangione's flugelborn and Chris Vadala's saxes and flutes were alternately biting and soft, and Charles Meek's bass was strong and provided an energy that propelled the set.

Mangione is an interesting performer and composer but he would do well to resist the sweetness that dulls the emotion of his musicians and his music.