By Bill Rigby and Christian Plumb SEATTLE/NEW YORK (Reuters) – Speculation over Microsoft Corps succession plans refocused on internal choices on Wednesday, a day after the leading outside candidate, Ford Motor Co CEO Alan Mulally, took himself off the list of potential CEOs at the worlds largest software maker. The source asked not be identified because they were not authorized to speak publicly about the process to select a successor to long-time CEO Steve Ballmer, who in August announced his plan to retire. In late January, many Microsoft executives will be focused on the companys earnings, which are scheduled to be released on January 23. For months, Microsoft watchers had pegged Mulally as the odds-on bet to succeed Ballmer as chief executive at the dominant producer of software for desktops and laptops, which has faltered in making the transition to the fast-growing mobile phone and tablet markets.