By Yeganeh Torbati and James Pearson
SEOUL (Reuters) - The liberal South Korean politician most likely to become the country's next president would, if elected, review how the government would deploy an advanced U.S. missile defence system and would consult China, two of his top advisers said on Friday.
If Moon Jae-in, front-runner for the May 9 presidential election, reverses policy on the deployment of the Terminal High Altitude Area Defence (THAAD) system, it will place him at odds with the United States, South Korea's biggest ally.
The conservative government of impeached president Park Geun-hye agreed to deploy the THAAD to guard against attack by North Korea, but the decision sparked outrage in China, which responded with restrictions on some companies doing business with and in South Korea.
China says the system's radar can be used to spy into its territory.
Moon would likely "do a review of the validity of the decision", Choi Jong Kun, an adviser to Moon on foreign policy told Reuters. "While doing it, he will consult with the United States, as well as China."
"At the end of the day, if the reality unfolds in a way that South Korea's national security and the economy were damaged because of the THAAD, not because of the North Korea issue, then it's not really a rational situation, is it?"
The comments are at variance with a tough stand taken by the new U.S. administration on North Korea.
U.S. Secretary of State Rex Tillerson, visiting Seoul for the first time since taking office, said on Friday a U.S. policy of "strategic patience" with North Korea has ended and military action would be "on the table" if North Korea if Pyongyang took action to threaten South Korean and U.S. forces.
Tillerson also said he expected the next South Korean government would "continue to be supportive" of THAAD.
A Pentagon spokesman said THAAD deployment was "a critical measure" to defend South Koreans and U.S. forces against North Korean missiles.
China is South Korea's largest trading partner and the dispute over THAAD has left shopping districts in Seoul devoid of their usual crowds of Chinese tourists.
In China, the row has led to a freeze of South Korean television dramas and music, and product boycotts.
Moon, a liberal facing little in the way of a significant conservative challenger, said in a debate this week China should stop the economic retaliation and South Korea had to make diplomatic efforts to assuage Chinese anger.
"It's only right for the THAAD deployment issue to be decided by the next administration," Moon told foreign media recently.
A 63-year-old human rights lawyer, Moon has said he will extend an olive branch to North Korea if elected and visit Pyongyang before making a trip to the United States.
Just two North-South summits have been held since the 1950-53 Korean war.
Choi said the decision to deploy the THAAD battery had been made hastily. China's reaction was foreseeable and yet was largely ignored by Park's government, he said.
"We had a strategic partnership with Beijing, until this THAAD issue," Choi said. "Our relationship had been pretty OK and pretty good."
Kim Ki-Jung, another foreign policy adviser to Moon, said he had tried to convince U.S. military officials and diplomats in Washington last month that the deployment of the THAAD should be left to the leader who succeeds Park.
"We are going to acknowledge that two governments made an agreement ... but the actual process of deployment, that should be given to the next government," he said.
Instead, the United States started to deploy the first elements of the system this month, after North Korea fired off four ballistic missiles into the sea off northwest Japan.
Moon has criticized the two former conservative presidents – Park and her predecessor, Lee Myung-bak - for derailing progress made in inter-Korean relations under previous liberal administrations.
He calls for a "two-step" approach on North Korea, with talks leading to "economic unification" and ultimately "political and military unification."
His viewpoints could spark friction with Washington, but Moon would have no problem distancing South Korea's interests from those of the United States, Kim said.
"The basic assumption is that we are going to maintain the success of our bilateral alliance," Kim said.
"We are going to keep it ... as long as we admit that South Korea is not the 51st state of the United States. We are an independent country, we have our own national interest, and we should have our own foreign policy strategy."
(Additional reporting by David Brunnstrom in Washington; Editing by Robert Birsel and Raju Gopalkrishnan)