Career diplomat Thomas Pickering was sworn in Monday as the U.S. ambassador to the United Nations and given a mandate by President Bush to put human rights high on the agenda. Secretary of State James Baker administered the oath to Pickering with Bush and his wife, Barbara, and Vice President Dan Quayle standing by. "I take the United Nations very seriously," said Bush, "and I'm pleased with the changes that have taken place, particularly on the financial situation." The president said, "I want Ambassador Pickering to give the question of human rights a high profile at the United Nations."