Gov. George E. Pataki of New York is headed to Iowa this weekend for what associates described on Thursday as an exploration of whether he should run for president in 2008, reflecting what they called an increased likelihood that he would forgo a bid for a fourth term next year and turn to the national stage. Gov. George E. Pataki could grab the votes of G.O.P. moderates. Mr. Pataki's associates said he viewed the trip - as part of a visit by him to a National Governors' Association meeting, taking place in a state that begins the presidential selection process...