Susan Rice, U.S. ambassador to U.N., takes center stage in debate over Syria violence UNITED NATIONS - Over Thanksgiving last year, Susan E. Rice, the U.S. ambassador to the United Nations , traveled with her husband and two children to Rwanda. It was part vacation - a chance to see the magnificent bird and gorilla population. But it was also a somber opportunity to visit the memorial honoring more than 800,000 people who died in the largest mass killing in modern times as the world looked on passively. Rwanda's 1994 genocide was a watershed for Rice. At the time, she was a 30-year-old National Security Council official in the Clinton administration, which stymied international efforts at the United Nations to respond militarily to the slaughter. Rice took the failure to heart. But the lessons of Rwanda have offered an imperfect guidebook as Rice weighs the use of U.S. diplomatic and military power. She helped rally support for action in Libya, where the United States helped topple a regime that had threatened to commit large-scale killings. But she has gone the other direction on Syria, with President Obama resisting calls for intervention there as thousands die in the fight against the government of President Bashar al-Assad. The prospect of international action to halt the violence in Syria will be one of the most pressing issues as the U.N. General Assembly convenes its annual debate Tuesday and Rice moves to center stage as the chief defender of U.S. policy toward Syria as well as the issue of Iran's ongoing nuclear efforts. In a lengthy interview last week, Rice said that her image as an interventionist has been overstated and that so has the impact of Rwanda on her deliberations on national-security and foreign-policy issues. Her approach as policymaker, she said, is to "bring analysis and rigor and elbow grease" to every problem. When Rice arrived in New York in January 2009, she had a reputation as a foreign-policy hawk, a passionate advocate for the use of American military force to halt atrocities in Darfur. While thousands were being slaughtered in the Darfur region of Sudan, she argued for U.S. military intervention in newspaper articles and congressional testimony. "If anybody thought that I was going to be a bomb thrower or a wild-eyed advocate of military intervention, they don't know me," she said. There is no one-size-fits-all. As Obama's longest-serving foreign-policy adviser, Rice, 47, is seen as a potential candidate to replace Secretary of State Hillary Rodham Clinton if the president wins a second term. Rice is charming, down to earth, quick with a joke, a proud mother who brags about her children. She was a Rhodes scholar and earned at doctorate in philosophy at Oxford University. As U.S. ambassador, she also has a reputation as a dominant, and sometimes domineering, force among her diplomatic peers. She blusters, she cajoles and she curses, participating in high-octave exchanges over Iran and Syria with Russia's U.N. ambassador, Vitaly Churkin. One council ambassador described her variously as "the bulldozer" and "the headmistress."