Some Waterbury, Conn., residents are up in arms over the possibility that MGM's movie version of "Union Street," starring Jane Fonda, may be filmed there early next summer. They object to Fonda because of her anti-war stance during the Vietnam War. Gaetano Russo, organizer of the anti-Fonda campaign said, "We want Jane Fonda to know she hasn't acted as a good American, and we don't want any part of her." Other protest activities: public statements from area veterans' groups; "We're not Fonda Hanoi Jane" bumper stickers and letters to the local newspaper. Fonda's Los Angeles spokesman had little to say about the fracas. "It's story with a lot of sizzle but not much steak," he said. "This is a first. . . . It's a manufactured story. It's one guy (Russo) trying to create a story and a conservative local paper. It's taken on a life of its own. But that doesn't necessarily mean it's real."