Senator Hillary Rodham Clinton mixed presidential gravitas and familiar talking points in the second and final debate of her re-election race yesterday, assertively challenging Bush administration policy on Iraq, Iran, and North Korea while carefully defending her own record on abortion rights. As in the first debate on Friday against her Republican challenger, John Spencer, a former mayor of Yonkers, Mrs. Clinton’s poise bordered on the monochromatic: She offered no new big ideas about the future of New York, she appeared engaged and mostly unflappable, and she used language that fell somewhere between safe and scripted.