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By Caren Bohan and Patricia Zengerle
SEOUL (Reuters) - U.S. President Barack Obama said he was willing to help North Korea repair its economy and end decades of international isolation if Pyongyang stopped a cycle of threats and finally moved towards nuclear disarmament.
Speaking to reporters at the end a week-long Asia tour, Obama said he and South Korean President Lee Myung-bak agreed the North must end a pattern of provocations that simply ended up with demands for more concessions but never resolved the central problem.
The two leaders also pledged to work to secure approval by their respective legislatures for their own free trade deal, signed more than two years ago. Lee said he was ready to discuss the main issue holding up ratification -- opening up the auto market.
"Our message is clear. If North Korea is prepared to take concrete and irreversible steps to fulfil its obligations and eliminate its nuclear weapons programme, the United States will support economic assistance and help promote its full integration into the community of nations," Obama said.
The talks were among the least problematic for Obama on his Asian tour that started in Japan, where divisions remain over the location of a U.S. military base, and also took in China, where he barely bridged divides on trade, currency policy and Tibet.
Obama and Lee have piled pressure on the destitute North by targeting its finances and telling Pyongyang it will win massive rewards if it abandons its atomic ambitions.
"The thing I want to emphasise is that President Lee and I both agree we want to break the pattern that existed in the past, in which North Korea behaves in a provocative fashion, and then is willing to return to talk ... and then that leads to seeking further concessions," Obama said.
He said he would send his first envoy to North Korea on December 8 to press Pyongyang to return to talks, frozen for almost a year, with regional powers to give up building a nuclear arsenal.
Analysts said he would not have agreed to it if he was not sure Pyongyang would reciprocate by returning to talks.
North Korea rattled the economically powerful region just ahead of Obama's first visit to Seoul since taking office by sparking a naval fight with the South and telling the world early this month it had produced a fresh batch of arms-grade plutonium.
But it has toned down its normally strident anti-U.S. rhetoric since Obama began his trip to Asia a week ago. Lee said he held out hopes for a deal with the reclusive neighbour under which it would end its decades-long ambitions to build a nuclear arsenal.
"I hope that by accepting our proposal, the North will secure safety for itself, improve the quality of life for its people, and open the path to a new future," Lee said.
Thousands of cheering South Koreans lined the streets of downtown Seoul as Obama's motorcade drove by.
Police stopped one group of anti-Pyongyang protesters setting fire to a North Korean flag as the Obama convoy drove through the centre of Seoul, barely 40 km (25 miles) from the border that has divided the two Koreas for more than half a century.
Obama was scheduled to speak to some of the 28,000 U.S. troops stationed in the South before flying home.
North Korea argues it is those troops that force it to develop nuclear weapons as protection from attack.
"The U.S. imperialist aggressor forces' presence in South Korea and their daily intensifying moves for a war of aggression against the DPRK (North Korea) are the main factor of disturbing peace and security on the Korean Peninsula," the North's official Rodong Sinmun daily said in a commentary.
One area of conflict between the allies has been a free-trade deal struck under President George W. Bush and yet to be approved by legislatures in either country. Studies said it could increase their $83 billion (49.6 billion pounds) a year in two-way trade by about $20 billion.
Obama said on Wednesday he wanted to iron out remaining issues with Lee on the trade pact and that the agreement could benefit U.S. exporters.
"I want to get the deal done," Obama said in an interview with Fox News.
Asked if he thought the agreement could be passed next year, he said: "The question is whether we can get it done in the beginning of 2010, whether we can get it done at the end of 2010. There's still some details that need to be worked out."
South Korea insists it will not renegotiate the deal, the biggest trade pact for the United States since the NAFTA accord of the mid-1990s with its immediate neighbours. But Seoul has left the door open for discussions for side deals on areas such as the auto trade, a sticking point in U.S. Congress approval.
"If automobiles are a problem, we are in a position to discuss them again," South Korea's Lee said.
(Additional reporting by Lee Jae-won, Jack Kim, Jon Herskovitz, Christine Kim and Jonathan Thatcher in Seoul and Jeff Mason in Washington; Writing by Jack Kim; Editing by Jonathan Thatcher and Alex Richardson)