Will Smith is looking to start work this summer on the Francis Lawrence-directed “I Am Legend,” a move that would give Warner Bros. a big summer 2007 tentpole. Pic originally wasn’t supposed to get under way until early next year.Move would amount to a slot swap with “Tonight, He Comes,” in which Smith was slated to star this summer. Gabriele Muccino took over the helm of that pic after Jonathan Mostow dropped out. Since Muccino is editing Smith starrer “The Pursuit of Happyness” for a Sony release in December, the studio pushed its superhero-in-existential-crisis pic until next year. WB wants to fill Smith’s vacancy, but it’s not easy. “Legend” is a logistically complicated post-apocalyptic film about the last healthy man battling blood-sucking mutants in New York.