Roh indirectly confirmed the demand had been made, but gave no further details. Media reports said Seoul was under pressure to send a brigade of about 3,000 troops.
Roh spoke as anti-war activists threatened to ignite nationwide protests to dramatize their opposition to the dispatch of South Korean troops.
"This is a very sensitive issue, so we must make a very careful review," Roh told a cabinet meeting, according to government spokesman Cho Young-Dong.
The issue of sending troops overseas is a politically charged one in South Korea, sharply divided between proponents and opponents of the US-led war in Iraq.
Civic groups said they would stage a mass anti-war rally next week in Seoul, while conservative groups urged the government to comply with the US request.
"Don't dispatch combat soldiers," read one placard during a rally by 50 activists near the offices of President Roh.
The protestors shouted anti-US slogans as riot police and security guards formed a human barricade to stop the march some 100 meters (yards) away from the president's office.
They scattered copies of a statement accusing US President George W. Bush of dragging South Korea into "a war of aggression" in Iraq.
North Korea joined the fray, denouncing the US request as "an intolerable criminal act" and urging South Korea to resist US pressure.
Minju Joson, published by North Korea's cabinet, accused Washington of wanting South Korean soldiers for "cannon fodder in Iraq as it did during the Vietnam war of aggression."
"The South Korean authorities should not yield to the US unreasonable pressure but withdraw their troops already dispatched to Iraq without delay and take an independent measure of rejecting the demand for additional dispatch," it added.
A pro-US conservative civic group, the Free Citizens Alliance of Korea, urged the government to send South Korean troops to Iraq.
"The dispatch of troops to Iraq will contribute to the enhanced alliance between South Korea and the United States, which have been at odds over the North Korean nuclear issue," the group said.
The South Korean media said the issue highlighted the rift between liberal and conservative groups over relations with the United States, South Korea's closest and oldest ally.
It is part of a wider debate on the need for the presence of US troops in South Korea and US policy on North Korea's nuclear ambitions.
"The government must make a comprehensive evaluation about what national benefits the dispatch of troops would bring. It must calmly study international opinion about the move and what we would gain from the United States," the JoongAng Ilbo newspaper said.
Roh, elected earlier this year on a wave of anti-US protests, backed the dispatch of 675 South Korean non-combatants, including army engineers and medics, in May to help rebuild post-war Iraq.
But it cost him support from younger voters, many of whom see no need for the US to keep 37,000 troops based in South Korea and view Washington as too hard on North korea.
US Defense Secretary Donald Rumsfeld told CBS television Sunday he wanted up to 15,000 additional international troops in Iraq under a new United Nations resolution.
Currently, the United States is stationing a 130,000-strong force in Iraq, backed by 21,000 troops from 21 countries. Britain and Poland have a division-level presence.
The United States is also asking other countries, including India, Pakistan and Turkey, to send combatants to maintain peace in the war-torn Middle East state, according to the media reports.