President Obama said Friday he would nominate Robert Hormats, a vice chairman of Goldman Sachs International, to a top economic position at the State Department. Mr. Hormats, 66, will be under secretary of state for economic, energy and agricultural affairs. He was deputy trade representative from 1979 through 1981 and held other posts at the State Department throughout his career. Hillary Rodham Clinton, the secretary of state, said in a speech on Wednesday that she hoped to make economic policy and trade a larger part of United States diplomacy.