Seeking to reassert the State Department's role as the primary agent of Washington overseas, Secretary of State Hillary Rodham Clinton on Wednesday announced an ambitious overhaul of diplomacy and development. And she promised to do it without spending a lot more money. Mrs. Clinton, in presenting a two-year review that has been one of her signature projects, declared that "leading through civilian power saves lives and money." Among key changes is a heavier emphasis on resolving conflicts and a pledge to reinvigorate the United States Agency for International Development.