NATIONAL SECURITY and foreign policy have rightly stood at the center of this presidential campaign. The nation is at war, American soldiers are dying daily in a complex and controversial conflict in Iraq, and the incumbent has shifted American approaches to both allies and enemies in bold and sometimes polarizing ways. All this accounts for much of the unusual passion that seems to have been aroused by this election -- emotion that we hope will find expression in a large turnout across the country today. It also explains the intense interest with which much of the rest of the world will join Americans in anxiously awaiting the results. And it places a special burden on either President Bush, should he be reelected, or Sen. John F. Kerry. Once the outcome is known, the election's winner should speak quickly and clearly to the nation, and the world, about where the United States is headed.

The challenge may be greatest for Mr. Kerry, should he succeed in ousting Mr. Bush. A change of presidents in wartime will raise the question of whether the country's commitment to victory remains firm, especially because Mr. Kerry has founded his campaign on critiquing Mr. Bush's performance as commander in chief. Mr. Kerry has been forceful in promising an unrelenting war against al Qaeda. But with Iraq at a crucial juncture, he must also send the message that his inauguration will not mean a retreat from America's commitment to hold elections and defeat extremist movements there. Enemies who have all but openly wished for a Kerry victory, such as the regime of North Korea, need to hear the new president reiterate his message that he will not relieve the pressure on them to give up weapons of mass destruction and stop supporting terrorism. Mr. Kerry should also stress that the United States will have only one commander in chief between now and January -- and that even if defeated, Mr. Bush should not flinch from the duty.

A victorious President Bush will have the option of declaring his military and diplomatic policies vindicated, and pressing ahead with them unaltered. In the case of Iraq, this would make sense, because in the short term there are few options other than the elections now being planned and the training of security forces now underway. But more broadly, Mr. Bush would be making a mistake to signal continuity. It is no secret that many governments of U.S. allies around the world, and especially in Europe, are hoping for Mr. Bush's defeat. If he is reelected, their first instinct may be to conclude that there will be little chance of improving relations with Washington during the next four years. Proponents of a Europe that unites itself around opposition to the United States could be greatly strengthened. Mr. Bush could head off this backlash by quickly pledging to make the rebuilding of U.S. alliances a priority of his second term and by promising to consult more often and more carefully with traditional American partners. If he is to manage the tremendous challenges he will face in Iraq, Iran, North Korea and elsewhere, Mr. Bush will need more international help. He would do well to say so immediately.