A GIFT OF LAUGHTER is promised by Bill Cosby, who has agreed to perform without pay for the benefit of Carnegie Hall. He will be on stage there Nov. 29, qualifying himself as a member of the Andrew Carnegie Society for his ``leadership gift.'' His name will be added to a plaque honoring special donors. A NEW PRODUCTION OF `WAR AND PEACE' is planned by Seattle Opera. A Soviet conductor and coach have been hired to work with the American director and designers of the production of the Prokofiev opera. It will be staged in July 1990, when Seattle will also be host to the Goodwill Games. RADIO CITY MUSIC HALL has scheduled the opening of its ``Magnificent Christmas Spectacular'' for Nov. 11. The all-live stage show has been presented annually since 1979. More than 900,000 people are expected to attend the show, which runs through Jan. 4. A WIDER AUDIENCE IS SOUGHT by ``USA Today: The Television Show,'' which will begin weekly telecasts in China sometime in January. The program will be seen on stations reaching 300 million viewers. Syndicated in the United States to more than 150 stations, the program has already been sold to 13 other countries. A FOUR-PART TELEVISION SERIES called ``Secret Intelligence,'' produced by station KCET, Los Angeles, will be aired weekly starting Jan. 23. Programs will deal with history as well as recent events in the intelligence field.