In a sudden shift of gears, Gene Saks is out and Michael Kidd is in as director of “The Goodbye Girl.”The Neil Simon-Marvin Hamlisch-David Zippel tuner is trying out at the Shubert Theater in Chicago and slated to begin Broadway previews Feb. 13 at the Marquis. Saks has directed much of Simon’s work, but sources at the theater say the two had a blow-up in front of the cast on Jan. 5 over the way the show was–or wasn’t–coming together. There is also a sense in the company that Bernadette Peters hasn’t settled into her part as smoothly as co-star Martin Short. The show opened last week to several positive notices, though Richard Christiansen in the Chicago Tribune called the show a “muddle.” Kidd, 73, saw the show twice and returned to California yesterday to devise game plan, while rewrites are under way. The authors are at work on a new opening number to replace the one that’s already been thrown out.