Behind the White House critique of the Israeli assassination: An administration official acknowledged that a change of tone was chosen only after a torrent of criticism erupted throughout the Arab world, and was then joined by condemnations from the European Union and Britain, Washington's closest ally in the Iraq war. Those officials said the Hamas leader's death had jolted administration officials just as they were accelerating plans for a highly visible and politically significant visit by Israel's prime minister, Ariel Sharon, to Washington, perhaps next month. An improvement in any case.