Representatives of five newspapers (including The New York Times) and the Associated Press news service have asked that documents in the Michael Skakel case be made public. Skakel, a nephew of the late Robert F. Kennedy, has been charged in the 1975 murder of his neighbor, Martha Moxley. Both were 15 at the time. David Fein, an attorney representing the press, told Stamford, Conn., Judge Maureen Dennis yesterday that Skakel’s court file — containing evidence that led to his arrest last January — should be opened now that Skakel is of legal age and because the public has a right to know about the case. “What we are seeking is the same material that would be available if this were an adult criminal case,” Fein told the magistrate. The state prosecutor told Judge Dennis that he did not oppose the documents being made public. Neither the state prosecutor nor Skakel’s attorney object to Skakel’s arrest warrant being made public, though Michael Sherman, who represents Skakel, does object to the use of several anonymous witnesses in the warrant.