WASHINGTON — Congressional Democrats savoring their return to power pledged yesterday to work closely with President Bush on a legislative agenda but demanded a change in course on Iraq and new directions on policies from the minimum wage to stem-cell research. The Democratic victories spell trouble for the hopes of the interim U.N. ambassador, John Bolton, for Senate confirmation, and greatly complicate President Bush’s efforts to appoint conservatives to the federal bench. More than anything else, public unhappiness over the Iraq war powered the Democrats’ success Tuesday, according to exit polls, but it was unclear yesterday how much the new Congress will or can do about the conflict. Senator Reid, a Democrat of Nevada, called on Mr. Bush to “convene a summit of congressional leaders” to discuss the war. “We’ve got to work together to change direction in Iraq,” Mr. Reid said.