Obama, winding up his weeklong Asian journey, was expected to emphasize the two nations' unified efforts to prod a defiant North Korea out of its nuclear-weapons program. He's also welcoming South Korea's return to helping U.S. efforts in Afghanistan.

Obama landed last night in South Korea, embarking on perhaps the easiest leg of his whirlwind four-country trip, which has taken him away from Washington for the longest stretch of his presidency. He made brief stops in Tokyo and Singapore before a longer, ceremony-filled visit to China.

Strongly pro-U.S., Lee took office in South Korea in early 2008, a year before Obama, and relations between the two countries have been improving. The tenure of President George W. Bush had seen anti-American sentiments become more common here.

A remaining sticking point has been trade. To South Korea's dismay, a free-trade agreement that was signed in 2007 by the two governments under previous leaders has been stalled ever since in Congress.

Obama and Lee were to spend about three hours together at the Blue House, South Korea's version of the White House.

Obama then has a brief rally at Osan Air Base outside Seoul with some of the 28,500 U.S. troops who are stationed in South Korea. It will be the third time Obama has addressed U.S. troops with his decision still pending on how many more Americans to send into the Afghanistan war.

Lee's government recently announced plans to expand a reconstruction team now helping to rebuild Afghanistan and to dispatch police and troops to protect them, two years after withdrawing all forces following a fatal hostage crisis.

Dozens of anti-war protesters rallied outside the U.S. Embassy yesterday chanting "no more South Korea troops to Afghanistan." Later, though, more than 100 people waved U.S. and South Korean flags and yelled, "Welcome, Obama, USA."

Obama and Lee are united in their impatience with North Korea's habit of making overtures, getting rewards and then backtracking to raise tensions again, and the two leaders were expected to discuss next steps in detail.

Seoul, fearing a military strike over its border or a rush of refugees from the North, has historically resisted a sterner approach toward ending the impasse over nuclear weapons - with it and China generally less interested than the U.S. and Japan in pursuing more sanctions. Those nations, as well as Russia, are in the six-party talks with North Korea over the active weapons program it has in defiance of U.N. Security Council resolutions.

Lee, though, has changed tack, talking of a "grand bargain" in which Pyongyang would get a one-time offer of concessions to replace the step-by-step process that has yielded little so far.

Obama, too, has made much of his desire to take a different approach. North Korean leader Kim Jong Il said the country would return to the six-party process it abandoned earlier this year only if Washington engages separately in one-on-one talks with the North. Days before Obama's arrival in the region, administration officials said Stephen Bosworth, the U.S. special envoy for North Korea, would visit Pyongyang on an unspecified date, probably this year.