Backing off denials that he had lobbied firms that do business with the city to help fund the Democratic National Convention, Mayor Thomas M. Menino now acknowledges he personally asked at least two companies with city contracts to pony up for the 2004 event. Menino had told the Herald that during fund-raising sessions at the Parkman House, he and U.S. Sen. Edward M. Kennedy placed joint calls to officials from Liberty Mutual Group and State Street Corp.