Roh instructed his cabinet to consider "real economic benefits" in forging a free trade agreement (FTA) with the United States, saying the accord should be "thoroughly based on practical national and public interests.
"If it's not in our interests, we are not going to sign it," he said, according a media pool report.
Roh's instruction came a day after US and South Korean negotiators wrapped up their eighth and final round of free trade agreement talks here.
Despite a wide gap on some sensitive issues, both sides expressed confidence that they could strike a deal by the end of this month through informal talks.
The deal, if agreed, would be the biggest since the 1993 North American Free Trade Agreement.
US-South Korean bilateral trade reached 74 billion dollars in 2006.
US negotiators must submit any FTA deal to Congress by April 2 for a 90-day review before President George W.
Bush's "fast-track" trade promotion authority expires on July 1.
Presidential officials