Justin Timberlake is expanding his movie creds with an action hero role in the war movie Stop the Loss. "Justin is thrilled about getting his first leading role. It is a huge challenge for him and he's excited as well as nervous," a source says. JT will be playing a tough renegade soldier in the flick. And what about the album he's working on? The source says, "Justin will have to work quickly to finish the songs. He has been in the studio but he won't have much time once he starts filming."