Alan Arkin and Kristen Stewart at Toronto Film Festival I never said it. Whatever it is. Those were the first words out of Alan Arkin as he walked into a room at the Shangri-La Hotel here on Friday morning. At 78, Mr. Arkin has been around long enough to poke fun at a film festival circuit he mostly avoids. But he does like Toronto - "How could I not like Canada?" he said. "They gave me two Canadian academy awards" - and he was in a playful mood as he prepared for the premiere of his new movie, "Argo," on Friday evening. He was also more than willing to do his bit for the film, which is to be released commercially by Warner Brothers on Oct. 12. Mr. Arkin is not exactly the star of the movie, which tells a not entirely serious but mostly true story set against the backdrop of the 1979 hostage crisis in Iran - not somewhere you'd normally look for laughs. Directed by Ben Affleck, who also plays the lead role, "Argo" was a surprise hit during a sneak preview at the Telluride Film Festival in Colorado last week. But Mr. Arkin was nowhere near the place. "It was Ben's first time out with the picture, and my sense was he didn't want me around," said Mr. Arkin, who spoke as if he'd been writing the dialogue for his own characters in the dozens of movies he's made over the years. As Mr. Arkin and any number of stars will attest, it is not all fun and games on the festival circuit. Kristen Stewart did some hard work here on Thursday night, as she showed up for a red carpet screening of "On the Road." It was her first formal public appearance since the messy, excessively chronicled meltdown of her relationship with her "Twilight" co-star Robert Pattinson. Ms. Stewart was stuck on the red carpet for 45 minutes or so, as "technical problems" - so described by Piers Handling, the festival's chief executive - delayed the jam-packed screening for which she had arrived. In a sheer black dress with blood-red flowers and stiletto heels - no scarlet letter for this woman - Ms. Stewart gamely worked a gallery of fans on her left and a gaggle of professional photographers on her right. Strobes flashed, publicists bustled, and only a handful of usually polite Canadian film fans resorted to boos and some mild heckling. "On the Road," an adaptation of the Jack Kerouac novel by the director Walter Salles, was poorly received at the Cannes film festival in May, but arrived here with some changes and did fine with Toronto's voracious film fans. In a question-and-answer session after the screening, Mr. Handling asked Ms. Stewart how she managed to identify with her character, the young wife of the roguish Dean Moriarty, played by Garrett Hedlund. "She really just loves so openly, and I think that's hard," Ms. Stewart said. That's hard to take. The crowd ate it up. When Mr. Handling threw the session open for a couple of questions, the first query, such as it was, signaled that Ms. Stewart had no enduring problem with her public. "Kristen, I'm a huge fan and I love you so much," gushed a young woman who had been handed the mike. Mr. Arkin was to be on the hot seat both Friday and Saturday, through the gala screening, a glittery after-party and, possibly the toughest part of the ritual, a half-hour or so in a mosh pit with the international press. Asked whether he had ever had his personal life go public, Mr. Arkin said yes, sort of. "I remember reading in the trades a long time ago that I was having an affair with Liza Minnelli, whom I'd never met," he explained. Just when he was beginning to enjoy the notoriety, Mr. Arkin added, "she dumped me, and I was depressed, but I'd still never met her." His advice for Ms. Stewart: "If she pays any attention to it, she will be very sorry." According to the generally reliable credits on the Internet Movie Database, "Argo" is Mr. Arkin's 15th film since "Little Miss Sunshine," for which he won an Oscar as best supporting actor in 2007. On Friday Mr. Arkin said that count seemed impossibly high. Then again, he acknowledged, he does work a lot, because of his mortgage payments. "Argo" is based on the story of Tony Mendez, a C.I.A. officer - played by Mr. Affleck - who managed to get a handful of Americans out of Iran during the hostage crisis by, almost unbelievably, pretending to be part of a film crew scouting locations for a movie fantasy called, of course, "Argo." Secret details of the operation were eventually declassified and became the basis for both a memoir by Mr. Mendez and a 2007 account by Joshuah Bearman in Wired. Those, in turn, became the underpinnings of a screenplay by Chris Terrio. In the film version Mr. Arkin doesn't exactly steal the show. But he and John Goodman, his screen sidekick, are pretty much what Rosencrantz and Guildenstern were to Hamlet: a couple of bit players who have a knack for finding center stage. Mr. Goodman plays John Chambers, a makeup artist who, before his death in 2001, became famous for his work on the "Star Trek" television series and films like "Planet of the Apes," and not so famous for a series of clandestine escapades in which he assisted Mr. Mendez from time to time. Mr. Arkin plays the producer Lester Siegel, who is recruited by Mr. Chambers to set up a fake Los Angeles production company, and help man the phones, just in case wary Iranian officials might ring to confirm Mr. Mendez's story. Mr. Arkin said Mr. Mendez told him during a chat here on Thursday evening that the Siegel character was mostly a composite, though somebody real was lurking behind it, somewhere. "But I wouldn't swear to any of that in a court of law," he added.