Carla Gugino, the young actress who portrays Michael J. Fox’s love interest, Ashley, on the freshman ABC sitcom “Spin City,” has left the show effective immediately in a split that both producer DreamWorks and a spokesman for the actress maintain is mutual.Gugino had received positive notices for her work in the Tuesday-night hit but was reportedly being increasingly overshadowed by Fox. Her final appearance will be on the show’s Dec. 17 episode. The first seg without Gugino — slated for Jan. 7 — will be the show’s 13th of the season. Sources report that this week, with the show on hiatus, “Spin City’s” writers are working up a plausible scenario to explain the Gugino character’s departure. The most likely storyline will have Ashley dumping Deputy Mayor Michael Flaherty (Fox) to pursue other career opportunities. The two have been living together as lovebirds this season, with Gugino playing a reporter assigned to cover City Hall. “The way it will likely play out is that Ashley will leave him and Michael will stay in a funk for several episodes,” one source said. “But even while he’s in the funk, he’ll be dating.” That desire to explore the romantic possibilities for Fox’s character is another factor that reportedly led to Gugino’s departure. A DreamWorks spokesman said, “We were all very pleased with Carla’s work, but unfortunately the storylines all began to gravitate toward the mayor’s office and away from the home, so the opportunities to develop her character were consequently very limited.” “Spin City” has been one of the few bright spots this season for ABC, ranking eighth for the season to date with a 14.1 rating and 22 share, albeit in the cushy sandwich between “Home Improvement” and “NYPD Blue” on Tuesdays. A spokesman for Gugino said that the actress “had to be convinced to do the show in the first place” and was in fact more consumed with building a film career, which her commitment to the series had halted. Gugino, who first gained notice in “Miami Rhapsody,” is appearing in four films that have either been released or are nearing release: “The War at Home” (in theaters), “Michael” with John Travolta (opening Christmas Day), and the independent features “Love Life” and “Jaded.” “Carla also wanted to come back from New York to L.A., where she lives,” he said. Gugino’s spokesman said the door remains open for a return visit to “Spin City” if it works out. “There’s no animosity on either side,” he said. “(Executive producer) Gary (David Goldberg) and Michael just wanted to see Carla happy. This is what she wants.” “Spin”-ster Carla Gugino is exiting the Michael J. Fox sitcom. Her spokesman and producer DreamWorks say the split is mutual.