After less than a year on the job, Robert Cooper resigned as president of TriStar Pictures, ending a frustrating period at the helm of the Sony label.Lucy Fisher, vice chair of the Columbia TriStar Motion Picture Group, and Gareth Wigan, co-vice chair of the group, will assume management responsibility for TriStar, the studio announced on Friday. It was uncertain if this would be a temporary arrangement or if he would be replaced. “Lucy and Gareth will work closely with the TriStar team to continue the production underway and to build on the studio’s momentum,” John Calley, president and chief operating officer of Sony Pictures Entertainment, said in a statement. Among the possibilities mentioned for Cooper were positions at PolyGram or DreamWorks. On Friday, Cooper said that his only immediate plans were “to go home and take a couple of weeks to consider what I’d like to do next.” Cooper’s exit came after what were a series of talks with SPE officials about his future. Cooper came to TriStar last summer from HBO Pictures, where he helped oversee the advance of the cabler’s telepic lineup into prestige fare including “Barbarians at the Gate” to “And the Band Played On.” When Cooper was hired last summer by Col TriStar Chairman Mark Canton, SPE was looking to shift the focus of the studio into handling more modestly budgeted fare, rather than blockbusters, with a yearly slate of pics made for $25 million or less. But things soon began to change. By early fall, Canton was gone, as well as SPE Chairman Alan Levine. The arrival in November of John Calley to head SPE was met with enthusiasm in the industry, but quickly there were rumors of clashes with Cooper. Both Calley and Cooper had downplayed a small tiff over “Fatherland” when Cooper was running HBO. Calley removed his name as producer. But as the months went on at TriStar, there was growing talk of Cooper’s frustration, mainly over his lack of autonomy over the TriStar label, and a perception that he was constrained in his ability to buy creative material. Under Calley, the corporate structure had changed from the typical studio approach. He adopted a much more collegial, committee approach to the process of making movies, whereas Cooper adopted a go-it-alone approach to his job. Studio insiders say that Calley is now interested in producing more highly budgeted pics. There also seemed to be a change in plans for the types of fare that would be made by TriStar. Some insiders say that Sony is moving toward event pics. In fact, the first film greenlit by the studio since Calley arrived was TriStar’s “Godzilla.” Other industry observers say Cooper never was able to get into the rhythm of the job, in part because he came from HBO Pictures, where there is more specialized development and contained budgets. Yet in announcing his departure, SPE brass said Cooper was instrumental in bringing together the creative components of such TriStar projects as the Chris Columbus-directed “Step-mom” starring Julia Roberts and Susan Sarandon; and “Jakob the Liar,” starring Robin Williams. Both pics were said to be very close to a greenlight at the time of his departure. “While Bob headed TriStar, he improved the overall packaging of key projects and provided enormous attention to improving the quality of scripts in development,” Calley’s statement said. They also said that he was responsible for managing the production of films such as “My Best Friend’s Wedding,” “The Mask of Zorro,” “Old Friends” and “Starship Troopers.” “I had a great time with him,” said “Troopers” director Paul Verhoeven. “He was extremely supportive. He understood the project and the large scope of the project. “In meetings, he would not voice his opinion differently than he would say when we were alone. What he said in the presence of four eyes was the same that he would say in front of 20 eyes.” “Jerry Maguire” also was released during his tenure, although the pic was greenlit and shepherded through production during the previous administration. Director Cameron Crowe said that Cooper was a big booster of the pic, even staying in town during Thanksgiving to work on its release. “He was great to me and great on ‘Jerry Maguire.’ “ There had been speculation on the lot that Sony is looking to merge creative staff at TriStar with Columbia. Already, business affairs and story development work in the same offices and share staff. But one Sony official said that such a move seemed unlikely.