By Michael Martina and David Brunnstrom WASHINGTON (Reuters) -U.S. President Joe Biden, his administration pledging to help Pacific island leaders stave off what it calls China’s “economic coercion,” promised them on Thursday to work harder with allies and partners to address their needs. Leaders and representatives from 14 Pacific island states are taking part in a two-day summit ending on Thursday. It is the first time the United States has hosted so many leaders of a region it has considered a maritime backyard since World War Two, but into which China made steady advances. Biden said the U…