A woman who has accused Bill Cosby of sexually assaulting her in the 1970s filed a defamation lawsuit Wednesday against the comedian, alleging he ‘‘publicly branded’’ her a liar through statements made by his lawyer and publicist. Tamara Green, 66, said in the lawsuit filed in federal court in Springfield (Cosby has a home in Shelburne Falls) that Cosby drugged and assaulted her when she was an aspiring model. Green first spoke publicly about the alleged attack in 2005. Green says after she did media interviews, Cosby’s lawyer and publicist made statements intended to expose her to public contempt and ridicule. The lawyer, Walter M. Phillips Jr., declined to comment. Messages left for the publicist, David Brokaw, weren’t immediately returned. Cosby is the lawsuit’s only defendant. Cosby, 77, has never been charged in connection with any sexual assault allegations. In 2005, Cosby settled a civil case filed by Andrea Constand, a former employee at Temple University. Green was one of a dozen women who were prepared to testify in Constand’s lawsuit.