Washington – Senator Barack Obama arrived in Afghanistan early Saturday morning, opening his first overseas trip as the presumptive Democratic presidential nominee, to meet with American commanders there and later in Iraq to receive an on-the-ground assessment of military operations in the two major U.S. war zones.

    Mr. Obama touched down in Kabul about noon, according to a pool report released by his aides. In addition to attending briefings with military leaders, he hoped to meet with President Hamid Karzai of Afghanistan before flying to Iraq later in the weekend.

    His trip was cloaked in secrecy, which advisers said was due to security concerns set forth by the Secret Service. His whereabouts have been unknown since he departed Chicago. He left Andrews Air Force Base near Washington on Thursday afternoon, according to a pool report, and turned up in Afghanistan on Saturday.

    Before he left the United States, he gave a brief outline of his trip to two pool reporters traveling with him from Chicago to Washington. No reporters accompanied him to Afghanistan.

    "Well, you know, I'm more interested in listening than doing a lot of talking," Mr. Obama said. "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, so it's the president's job to deliver those messages."

    Mr. Obama's arrival opened a weeklong foreign trip that includes visits to Iraq and two other stops in the Middle East as well as appearances in three European capitals. His tour of Afghanistan and Iraq are part of a Congressional delegation — similar to trips that Senator John McCain, the presumptive Republican nominee, made in the spring — in which he is joined by Senators Chuck Hagel, Republican of Nebraska, and Jack Reed, Democrat of Rhode Island, both of whom have been mentioned as possible vice presidential running mates.

    The international trip by Mr. Obama is intended to counter Republican criticism — and one advanced by Senator Hillary Rodham Clinton during the Democratic primary campaign — that he has too little experience in foreign affairs to serve as a world leader.

    His advisers said Mr. Obama chose to begin his trip in Afghanistan because he believes that the region is among the most important foreign policy challenges facing the United States.

    "Well, I'm looking forward to seeing what the situation on the ground is," Mr. Obama told reporters on Thursday before he left Washington. "I want to, obviously, talk to the commanders and get a sense, both in Afghanistan and in Baghdad of, you know, what the most, ah, their biggest concerns are. And I want to thank our troops for the heroic work that they've been doing."

    It is the first trip to Afghanistan for Mr. Obama, a member of the Foreign Relations Committee. This week, he proposed deploying about 10,000 more troops to battle resurgent forces in Afghanistan, a plan intended to shift the American military focus from the Iraq war to what he calls the central fight against terrorism.

    The proposal has become a centerpiece of Mr. Obama's foreign policy and a major point of disagreement with Mr. McCain, who maintains that both places are major battlegrounds and disputes Mr. Obama's suggestion that the war in Iraq has distracted the United States from its efforts in Afghanistan.

    Mr. McCain has suggested to voters that Mr. Obama lacks the experience to serve as commander in chief. He particularly criticized the Illinois Democrat for not having held a single hearing in his capacity as chairman of the Foreign Relations Committee's subcommittee on European affairs.

    "He's going to go to the American people and say, 'I want to be commander in chief,' " Mr. McCain told reporters on Thursday, "and yet he has been the chairman of the subcommittee that oversights NATO and he has never had a hearing, nor has he ever visited Afghanistan.' "

    But that criticism was dismissed this week by Senator Joseph R. Biden Jr. of Delaware, the chairman of the Foreign Relations Committee, who said issues related to Afghanistan were intentionally being addressed "at the full committee level."

    Mr. Obama's trip is drawing considerable attention in the United States and abroad. It is being carefully choreographed by his campaign strategists to coincide with a new television advertisement in 18 states intended to highlight his ideas on foreign policy and portray him as ready to serve as commander in chief, which is one area where polls show that voters give an edge to Mr. McCain.

    In addition to visiting Iraq and Afghanistan, Mr. Obama is extending his overseas tour, his first as a presidential candidate, to include a visit to Amman, Jordan, on Monday, followed by stops in Jerusalem, the Palestinian territories, Berlin, France and London.

    Now that Mr. Obama has decided to take the trip, the McCain campaign is not sure what to make of it. Jill Hazelbaker, the communications director for Mr. McCain, offered a hint of the Republican criticism of the trip on Thursday by dismissing it as "the first-of-its-kind campaign rally overseas." But Mr. McCain sought to temper the message, saying: "I'm glad he is going to Iraq. I am glad he is going to Afghanistan. It's long, long overdue if you want to lead this nation."

    Robert Gibbs, a senior campaign strategist for Mr. Obama, dismissed that suggestion. He said the trip was rooted in substance, rather than politics.

    "The trip is not at all a campaign trip, a rally of any sort," Mr. Gibbs told reporters on Friday. He said Mr. Obama would hold "a series of substantive meetings with our friends and our allies to talk about the common challenges that we face and the national security dangers for the 21st century."

    In the next week, Mr. Obama is scheduled to meet several foreign leaders, including German Chancellor Angela Merkel, British Prime Minister Gordon Brown, French President Nicolas Sarkozy, Jordan's King Abdullah, Israeli Prime Minister Ehud Olmert and President Shimon Peres and Palestinian President Mahmoud Abbas.