KABUL, AFGHANISTAN - Sen. Barack Obama arrived in Afghanistan on Saturday, opening a high-stakes foreign trip in a country that is increasingly the focus of his clash with Sen. John McCain in the presidential campaign over whether the war in Iraq has been a distraction in hunting down terrorists.

As Obama met with U.S. troops, military leaders and regional officials in eastern Afghanistan, he made no public statements in his first hours on the ground there, the first stop on a weeklong trip that will take him to Iraq, Israel and Western Europe.

But McCain quickly sought to raise questions about Obama's judgment on foreign policy, saying in a radio address Saturday that his Democratic opponent had been wrong about the increase in troops in Iraq, a strategy McCain said should be the basis for addressing deteriorating conditions in Afghanistan as well.

Obama flew to eastern Afghanistan, close to the border with Pakistan, to get a firsthand look at the region where U.S. troops are feeling the brunt of increased attacks from militants infiltrating the border from Pakistan. In selecting Afghanistan as the opening stop of his first overseas trip as the presumptive Democratic nominee, he was seeking to highlight what he says is its importance as the key front in the fight against terrorism.

The trip is intended to build impressions -- and counter criticism -- about his ability to serve on the world stage in a time of war. It carries political risk, particularly if Obama makes a mistake -- the three broadcast network news anchors will be along for the latter parts of the trip. There is also a political risk if he is seen as the preferred candidate of Europe or other parts of the world. But his advisers think the trip offers a significant opportunity for him to be seen as a leader who can improve America's image.

"I'm more interested in listening than doing a lot of talking," Obama told reporters before leaving Washington for a trip cloaked in secrecy because of security concerns. "And I think it is very important to recognize that I'm going over there as a U.S. senator. We have one president at a time."

Even as the fragile economy has emerged as the chief issue on the minds of voters in the United States, on Saturday the presidential race unfolded with a foreign policy debate taking place across borders and time zones, a reminder that the nation is at war and that the candidates offer very different backgrounds and approaches when it comes to national security.

Obama landed in Kabul just before noon Saturday, his aides said, after stopping to visit -- and play basketball with -- U.S. troops in Kuwait. In Afghanistan, he received a briefing from military commanders at Bagram Air Field and was scheduled to meet with President Hamid Karzai today.

While the Iraq war has been one of the dominant issues in the presidential campaign, Afghanistan has moved to the forefront of the foreign policy plans of both candidates. President Bush's agreement to a "general time horizon" for withdrawing U.S. troops in Iraq has opened the door to new consideration of strengthening the U.S. and NATO presence in Afghanistan, which Obama and McCain both agree on in principle.

For months, McCain has criticized his rival for failing to visit Afghanistan and taking only one trip to Iraq. Even on Saturday, in a radio address, McCain renewed his criticism and sought to minimize Obama's trip. "In a time of war," McCain said, "the commander in chief's job doesn't get a learning curve."

McCain, whose campaign spokeswoman suggested that Obama was embarking an on a "campaign rally overseas," said his rival was not going to Afghanistan and Iraq with an open mind. In his radio address, he said, "Apparently, he's confident enough that he won't find any facts that might change his opinion or alter his strategy -- remarkable."

In addition to his visit to Iraq, Obama is set to meet with a series of presidents, prime ministers and opposition leaders as he travels to Iraq, Jordan, Israel and three European capitals, including Berlin, where he is to give a major speech on Thursday. On the Afghanistan and Iraq leg of the trip, he has been joined by Sen. Chuck Hagel, R-Neb., and Jack Reed, D-R.I., both of whom have been mentioned as possible running mates for Obama.

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