ARIKIP:
The movie was a greatly edited/shortened version of the 3 parter "Saga of a Starworld".
According to "Battlestar Wiki" it wasn't originally in three parts:
"Saga of a Star World aired as a tv movie in a single installment on September 17th, 1978, and was thereby the only episode of the show which did not have a running time of approximately 50 minutes. With commercial breaks, the episode ran 3 hours. For subsequent television showings, in the USA and overseas, it was re-edited into three 50-minute episodes."
It appears that you're correct about it being shortened/edited for theatrical exhibition though.