WASHINGTON — Even as they campaign on their differences, John McCain and Barack Obama have been quietly recalibrating their messages on foreign policy in ways that often have moved them closer to the political center — and to each other.

The Republican and Democratic nominees, scheduled to meet in a kickoff presidential debate today if differences are resolved, hold decidedly differing outlooks on foreign affairs. McCain has stressed his readiness to confront adversaries; Obama has emphasized engagement and negotiation.

But on a striking list of particulars - including Russia, Afghanistan, Iraq — their differences have narrowed as Election Day approaches.

In part, the migration reflects the complexity of this year's national security issues, knotty problems that have defied solutions proposed by partisans on the left or right.

But the shift also reflects how they are increasingly focusing on uncommitted voters.

"Everybody's trying to grab the same voters in the middle," said a Democratic strategist who was not authorized to speak for the Obama campaign and did not want to be identified. "They're reading the same polls and competing for the same voters."

McCain has been tweaking his course as he tries to reconcile the twin objectives of looking like a strong commander-in-chief, but not one who might entangle the nation in unwanted wars. That stance answers polls showing voters want to avoid unnecessary military commitments, which are associated with President Bush.

Advisers and allies insist that it is the candidate of the other party who has been doing most of the shifting. But it is clear that each is making adjustments.

Take Russia. McCain greeted Russia's Aug. 7 invasion of Georgia with fiery denunciations of Moscow, while Obama called for restraint, and avoided assigning blame.

But in the days that followed, Obama became more and more critical of Russia. McCain, meanwhile, began to sound conciliatory notes at key moments.

Before his Sept. 4 Republican Convention acceptance speech, aides signaled McCain would come down hard on Russia; instead, he said Americans owed Georgia only "our solidarity and prayers" and promised "I will work to establish good relations with Russia, so we need not fear a return to the Cold War."

From the beginning of the presidential campaign, the two candidates have held similar views on issues like North Korea, expansion of the U.S. military and the treatment of suspected terrorists. They have moved closer on how to deal with Russia and Iran, on a proposed strategic alliance with India, and even on the U.S. troop surge in Iraq.

As recently as July, for example, McCain was arguing that the deepening insurgent threat in Afghanistan was not a result of a lack of U.S. troops but of Pakistan's unwillingness to properly patrol its border and deny militants a safe haven.

But on July 15, McCain echoed Obama's call for more troops. Thanks to success in Iraq, McCain said, it now was possible to send extra brigades to Afghanistan.

Obama, who built his campaign on his opposition to the Iraq war, has continued to modify his views on the conflict as polls show Americans view the troop "surge" and even the war itself more positively. The Democrat said this month that the surge, which he opposed, "has succeeded beyond our wildest dreams." However, he emphasizes that in his view the buildup has not produced its ultimate goal of political reconciliation among Iraqis.

Obama has long had serious reservations about the proposed U.S.-India civilian nuclear agreement, aimed at cementing an alliance between the two countries. Critics on both the political left and right worried the agreement would weaken international attempts to limit the spread of nuclear weapons by permitting nuclear trade with a country that developed its own nuclear bomb.

In 2006, Obama voted for amendments that threatened to upset the deal. But earlier this month, Obama signaled that he favored it and said that as president, he would work for it.

McCain, for his part, is putting distance between himself and his proposal for a "league of democracies." The idea was a hit among neoconservative supporters when McCain introduced it last year as a formal organization that could use military and economic power when the U.N. and other groups failed to act.

Last spring, McCain said it would be an ad hoc coalition that wouldn't use military force. Nowadays, he rarely mentions it. Some analysts believe McCain has tempered his message in response to signs of an inward-looking mood among voters.