Whether to deploy THAAD has emerged as a hot potato for the National Assembly's April session, which will begin from Tuesday.
The ruling Saenuri Party and the main opposition New Politics Alliance for Democracy (NPAD) have remained sharply divided over the issue.
The governing party held a meeting of its lawmakers Wednesday to draw up its stance toward potential deployment of a Terminal High Altitude Area Defense (THAAD) system in South Korea.
Ruling party floor leader Rep. Yoo Seong-min, a noted supporter for the deployment, told lawmakers, "The issue is directly related to the life of the people. The governing party will deliver its stance to Cheong Wa Dae after collecting various opinions of its members through free discussion."
He made clear that he does not intend to stick to his personal opinion about the issue.
"I want Rep. Kim Sung-chan, the governing party's representative of the National Defense Committee, to lead the discussion," Yoo said.
Yoo has so far openly talked about the need for the deployment, saying THAAD should be deployed at the earliest possible date to protect people from nuclear and missile threats.
His proposal for open debate has caused conflict with the presidential office, which is seeking to handle the issue through quiet diplomacy.
President Park Geun-hye talked about the advanced missile interceptor system for the first time Tuesday. She said, "What the government needs to do is secure enough information to make the overall and right judgment."
Some lawmakers who support Park were against Yoo during the party meeting in an apparent attempt to support the President.
For its part, the NPAD has expressed clear opposition to bringing the latest interceptor to the Korean Peninsula.
Rep. Ahn Gyu-baek, a member of the National Defense Committee, said, "The deployment had more disadvantages than advantages."
He also played down the view that the deployment will enhance the Seoul-Washington alliance, saying, "That is an impetuous argument."
The NPAD Chairman Rep. Moon Jae-in indirectly expressed his skepticism.
"The sincere independence of the country seems to be still far away," he said.
The THAAD system is widely regarded as the core of the U.S. ballistic missile defense (MD) system.
Washington hopes to bring its advanced missile interceptor into South Korea to better deal with missile threats from the North. But Seoul has never given a definite answer, apparently because it fears strong opposition from China, Korea's No. 1 trading partner.
China has been pressing South Korea to block the U.S. move, alleging that it could be used to nullify China's military strike capabilities.
Russia has also expressed opposition to the deployment.
Follow Jun Ji-hye on Twitter @TheKopJihye