It will be a party of poets, Pulitzer Prize winners and at least one writer who can legitimately call himself a genius. But don’t let Saturday’s guest list intimidate you. The Maine Writers & Publishers Alliance 40th anniversary party – “The Big Four Oh” – is meant to be casual and fun. “This is a quintessential summer party in Maine, so it’s come as you are,” executive director Joshua Bodwell said. “The Big Four Oh” celebrates Maine’s literary heritage and looks ahead to the future of the organization, whose mission is to enrich Maine’s cultural life through literature. The Saturday afternoon bash boasts a spectacular setting and a roster of literary stars, including Richard Ford, Richard Russo and Elizabeth Strout, all of whom have Pulitzers for fiction – Russo for “Empire Falls” in 2001, Strout for “Olive Kitteridge” in 2009 and Ford for “Independence Day” in 2010. There will be a two-time Newbery Medal winner, a National Book Critics Circle Award winner, a Kirkus Prize for Fiction winner and a New York Public Library Young Lions Fiction Award winner, among others. Jonathan Lethem, winner of the MacArthur Foundation “genius” grant in 2005, plans to attend, along with Maine’s outgoing poet laureate, Wesley McNair, and past poet laureate Betsy Sholl.