South Korean President Lee Myung-bak defends his hard-line strategy against the North, saying there are signs his approach is beginning to work. (Courtesy of the Blue House/South Korean Presidential Office)

Facing growing criticism that his hard-line stance toward North Korea has backfired, South Korean President Lee Myung-bak defended the strategy, and said there are signs his approach is beginning to work.

Lee has said that Seoul will provide aid and security to its neighbor only after Pyongyang denuclearizes. Speaking on Monday, he said that controversial strategy had yielded a breakthrough: In recent meetings between the Koreas, the North has been willing to discuss its nuclear program. Though talking about the arsenal is far different than dismantling it, the subject itself was previously off limits.

“There are some real changes we are detecting,” Lee said in an interview. “In the past, if we had dialogue between the two Koreas, it was never about nuclear weapons. The discussion was only about when and how much aid we would give.”

If Pyongyang agrees to a monitored shutdown of its nuclear weapons program, the concession would validate a strategy that has, in the short term, turned North Korea more dangerous, not more compliant.

Lee had hoped his stance would push North Korea to recommit to old denuclearization promises. Instead, the North has kept its weapons — and turned to China for the aid and investment it once got from Seoul. Intra-Korean relations hit a low point last year with two military attacks on South Korea, prompting calls domestically for Lee to soften his approach.

The hard-line strategy marked a dramatic shift from Lee’s two predecessors, who oversaw the 10-year “Sunshine Policy” period of aid, investment, and summit meetings with North Korean leader Kim Jongb Il.

Lee has spoken in recent months of a more “flexible” approach toward the North, but he denied on Monday he will reconsider his main principle: The North must commit to denuclearization as a first step for better relations.

Lee travels this week to Washington, where he is scheduled to meet with President Obama and address Congress on Thursday. Lee and Obama must determine whether it’s wise to maintain such a demand, given the dangers of withholding engagement while waiting for an unlikely concession. Lee said he expects “no meaningful changes” in the U.S. and South Korean approach, but some policymakers in both countries say the approach has only caused Seoul and Washington to cede influence over the cash-hungry authoritarian dictatorship.

“Of course my policy can receive criticism: It’s taken a long time,” Lee said. “It requires persistence. But we’re trying to fundamentally resolve the problem.”

In a wide-ranging interview at the president’s official residence, the Blue House, Lee called on the United States to increase its role in Asia, cooperating with China while also serving as a balance to China’s rise. During Lee’s four-day visit — his sixth trip to the U.S. as president — Congress is expected to ratify the U.S.-Korea free trade agreement, which was signed in 2007 but later renegotiated. That pact, which Korea also plans to ratify, “sends a powerful signal to the world” about U.S. engagement in Asia, Lee said.

The trade agreement, Lee said, also tightens the relationship between Seoul and Washington, whose militaries have cooperated for six decades on the Korean peninsula. “This is now an economic alliance,” Lee said.

Once the agreement takes effect, it will remove 95 percent of the tariffs between the countries, and the Obama administration predicts it will double exports to South Korea within five years. That would help the U.S. make up ground on China, whose exports to South Korea accounted for $117 billion in 2010 — more than three times the figure for U.S. exports.

As he nears his final year as president, Lee has given a few modest indications of new flexibility toward Pyongyang. In March, Seoul allowed certain South Korean organizations to resume humanitarian aid to the North. In August, Lee named a new chief minister for North Korean policy who vowed to create “an atmosphere for dialogue.” And twice in recent months, nuclear envoys from Seoul and Pyongyang have held meetings — the preliminary nuclear talks that Lee described as encouraging — though little detail was disclosed publicly, and Lee did not provide any in the interview.

Lee played down concerns that the United States and South Korea have lost the ability to influence Pyongyang, which has turned China into its major benefactor as Kim Jong Il passes power to his youngest son. Kim has visited China three times since 2010, once even spurning former U.S. president Jimmy Carter, who was in Pyongyang and wanted a meeting.

“It may look from the outside like the U.S. and South Korea are losing influence,” Lee said. “But when I see Chairman Kim Jong Il visit China, I always say that is a good thing — a positive thing. It gives North Korea a chance to learn about the Chinese experience” of economic opening.”