LOS ANGELES — In summers past, Warner Brothers used Comic-Con International, the premiere convention for comic book, science fiction and fantasy fans, as a marketing platform for movies like “Sherlock Holmes,” “300” and “Sucker Punch.”  Walt Disney Studios staged “Tron: Legacy” stunts there three years in a row. Last July, DreamWorks Animation paraded Will Ferrell, Tina Fey and other members of the “Megamind” cast through the convention.  This year? Warner’s main studio operation is bringing nothing. Ditto Disney and DreamWorks. The Weinstein Company, a perennial presence, will also sit this one out. Even Marvel Entertainment, whose panel for “The Avengers” was a highlight of Comic-Con 2010, is on the fence about whether it will mount a major presentation.  Comic-Con, as a growing number of movie marketers are realizing, has turned into a treacherous place. Studios come seeking buzz, but the Comic-Con effect can be more negative than positive. The swarm of dedicated fans — many of whom arrive at the convention in Japanese anime drag or draped in Ewok fur — can instantly sour on a film if it doesn’t like what it sees, leaving publicity teams with months of damaging Web chatter to clean up.  “It’s a red-letter opportunity, but you shouldn’t go simply because it sits there on the calendar,” said Michael Moses, co-president of marketing for Universal Pictures. “You have to be absolutely certain you have goods ready that can really make a difference for your film.”  Even a joyous reaction at Comic-Con, which takes place in San Diego from July 21 to 24, can skew expectations, as a platoon of studios learned last year, if hard-core enthusiasm doesn’t spill into the mainstream.  Warner got burned with “Sucker Punch,” which had fans vibrating with excitement in July but failed in its March release. The millions that Disney spent on “Tron: Legacy” at Comic-Con had a less-than-fantastic payoff. A stunt involving video of attendees trapped in coffins made a splash for Lionsgate’s “Buried,” but the film sold just $1 million in tickets when it opened two months later.  “Scott Pilgrim vs. the World” was the big alarm. That Universal movie was the belle of last year’s convention, and the studio spent heavily to make it so, draping the entire side of a skyscraper with an ad, for instance. Released just three weeks after the convention, “Scott Pilgrim” fizzled and the $60 million movie sold just $32 million in tickets.  Comic-Con, which attracts about 130,000 people, usually doesn’t lock in its schedule of presentations until two weeks before the convention — a practice that keeps studio publicists on edge, as they struggle to wrangle stars for appearances in slots that remain at a premium.  David Glanzer, the convention’s director of marketing, said he didn’t detect any major shift in the film industry’s stance toward Comic-Con.  “We get more and more requests, and have less ability to fulfill them,” he said, adding, “Not every studio comes every year.”  For certain, Big Hollywood will still be represented. Universal is plotting a stunt for “Cowboys & Aliens,” which has the advantage of a July 29 release date, when memories of a Comic-Con splash will be fresh. Paramount plans to trot out “The Adventures of Tintin: The Secret of the Unicorn,” with a possible appearance by its director, Steven Spielberg.  Twentieth Century Fox is expected to tackle Comic-Con head-on, particularly with its “Rise of the Planet of the Apes,” which arrives in theaters on Aug. 5. And Sony will roll out an aggressive promotion for its “The Amazing Spiderman,” even though the film won’t be seen until July 2012.  And the light schedule of some major studios leaves a void that newer players want to fill. Relativity Media, once a film financier and now a producer, is expected to make a push at the convention for “Immortals” and “The Raven,” while promoting “Shark Night 3-D,” which is bloodier than the convention usually tolerates.  Among smaller studios, Lionsgate, which won strong results last year for “The Expendables,” will be back; and Summit Entertainment will stage a panel for “The Twilight Saga: Breaking Dawn — Part 1.”  The industry has also realized that Comic-Con’s timing, in late July, is actually friendlier to TV shows, which are getting revved up for fall debuts.  Fox plans to increase its Comic-Con footprint, mounting promotions for at least 10 series, including “Terra Nova,” a dinosaur show produced by Mr. Spielberg. Warner’s Digital operation is planning to promote several original Web series, including “Mortal Kombat: Legacy,” and Warner’s TV division wouldn’t mind stealing the show.  “We’re certainly hoping to,” said Lisa Gregorian, chief marketing officer for the Warner Brothers Television Group, which plans to promote as many as 16 shows — including returning ones “Big Bang Theory” and “Chuck” — at the convention.  Still, even Ms. Gregorian, who said she had spent six months planning to reach fans at Comic-Con — whom she calls “evangelists” — doesn’t foresee her medium displacing the movies in the convention’s Hall H, which annually takes on the aura of a pop cinematic shrine.  “That’s a creative decision by the convention,” she said of the movies’ pride of place in the largest room. “We’re very respectful of that.”  A version of this article appears in print on June 13, 2011, on page B7 of the New York edition with the headline: Movie Studios Reassess Comic-Con. 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Comic-Con has long been a marketing platform for movie studios. But the convention’s effect often can be negative and the studios have noticed.