Here's a clip of the opening of the original movie with the song sung by Johnny Mandel for the movie soundtrack. According to Wikipedia, the song was written by 14 year old Mike Altman, son of the original film's director, Robert Altman.
http://www.youtube.com/watch?v=H2vguoy2aAY
During an appearance on The Tonight Show in the 1980s, Robert Altman said his son earned more than a million dollars for co-writing the song while he only made $70,000 for directing the movie.
I remember watching the movie when it was first released, but after watching MASH on TV for years I had nearly forgotten it. I need to rent the DVD and do a little reminiscing.
Rodger