President-elect Barack Obama and Senator Hillary Rodham Clinton on Monday will seal their rapprochement when he announces her nomination as his secretary of state, Democrats close to the process said Sunday. Mrs. Clinton, once considered the Democratic frontrunner for president, is flying to Chicago to appear together with the man who beat her for the nomination, a person close to Mrs. Clinton said. The sight of them together, as she joins his administration, would have been thought unlikely just weeks ago, but Mr. Obama concluded she would strengthen his team. At a time when the country remains engaged in two wars and still faces the threat of international terrorism, Mrs. Clinton will anchor a national security team with more of a centrist character than some of Mr. Obama's liberal supporters once hoped to see. In addition to her, Democrats said, Mr. Obama plans to announce that he is keeping Defense Secretary Robert M. Gates, who has run the Pentagon for the last two years, and will appoint Gen. James L. Jones, a retired Marine commandant, as national security adviser. Rounding out his national security team, Mr. Obama will name former Deputy Attorney General Eric H. Holder Jr. as his choice for attorney general and Governor Janet Napolitano of Arizona as secretary of homeland security, the Democrats said. Mr. Obama also will nominate Susan E. Rice, his foreign policy adviser and a former assistant secretary of state, as ambassador to the United Nations, a job that will be given cabinet rank, as it had under President Bill Clinton. The Obama and Clinton teams have been preparing the ground for this announcement for days. Mr. Clinton, who has extensive business and philanthropic interests around the world, agreed to a nine-point plan covering disclosure, vetting and other areas to avoid potential conflicts of interest, including for the first time the release of more than 200,000 donors to his foundation by the end of the year. That goes beyond the requirements of existing law. The Obama team has planned for a while to unveil the national security team after the Thanksgiving holiday, but the timing took on additional urgency after the terrorist attacks in Mumbai. The attacks, which killed at least 180, including six Americans, offered a stark reminder that for all of Mr. Obama's focus on fixing the economy, national security can capture a president's attention at any moment.