Whenever in his opinion the purposes of this subchapter would be promoted by a conference, the Surgeon General may invite representatives of as many State agencies, designated in accordance with section 291d of this title, to confer as he deems necessary or proper. A conference of the representatives of all such State agencies shall be called annually by the Surgeon General. Upon the application of five or more of such State agencies, it shall be the duty of the Surgeon General to call a conference of representatives of all State agencies joining in the request.