WASHINGTON (Reuters) - White House hopefuls Mitt Romney and Sarah Palin lead a narrower field of potential rivals for the 2012 Republican Party presidential nomination, according to a poll released on Thursday.The Gallup survey is the organization's first since Indiana Governor Mitch Daniels, former Arkansas Governor Mike Huckabee and real estate mogul Donald Trump opted out of the slowly evolving primary race.Read More... More on Elections 2012