H.N. Swanson Inc., the writer and director percentery, hired Larry Kennar away from the Maggie Field Agency.Kennar, 26, will bring most of his clients with him, including Joseph Bellissimo and Jeff LoGrasso, who wrote “White House Party” for Paramount, and Linda Vorhees, who penned “Crazy From the Heart” for TNT. Swanson prexy Thomas J. Shanks said Kennar gives the firm some strength in signing up-and-coming talent. “This kid is very bright and a real hustler,” Shanks said. “He really knows a lot of these young writers.” Prior to joining Field in 1991, Kennar was a freelance reader for MGM. He began at Swanson last Monday.