Roh's support for the US-led war has sparked friction with communist North Korea and triggered the biggest domestic challenge to his administration since he took office in February.

"For a peaceful solution to the North Korea nuclear issue, solid South Korea-US cooperation is very important," the president said in a speech to the National Assembly to rally support for sending 700 non-combattants to Iraq.

As Roh spoke, thousands of people protested outside the National Assembly building in the latest of several rallies across the country reflecting deep seated opposition to the US-led war.

Roh said it was in South Korea's interest to back the United States now, not because it was a principled act, but because the nation would need US support for a peaceful resolution to the nuclear crisis.

A majority of lawmakers support Roh, but have twice put off voting on the motion, fearing a backlash from the public. They were expected to put the motion to a vote either later Wednesday or on Thursday.

"I have decided to send troops. It is because the fate of this country and the nation are at stake," said Roh.

He said it was more important to strengthen South Korea-US relations rather than to "stand on principle and incur friction in bilateral ties."

Critics of the 56-year-old reformist president, many in his own party, say that supporting the war on Iraq implies backing for the US policy of preemptive military action, which Washington could invoke to launch an attack on North Korea.

Roh countered that the surest guarantee of peace on the Korean peninsula was solid ties with the United States under a 50-year-old alliance that has come under strain in recent months from anti-Americanism, and differences over how to handle North Korea.

Washington has said it is seeking a peaceful solution to the crisis triggered nearly six months ago but has not ruled out the military option.

Roh opposes military action or even the imposition of sanctions against North Korea which maintains that it will be the next target of a US attack once the Iraqi war is over.

"As you have seen in the Iraqi situation, the United States will not make its decision on the North Korean nuclear issue in line with principles," said Roh.

However, he said as long as South Korea opposed an attack on the North, "there will be no war on the Korean peninsula."

At one point, Roh seemed to agree with South Korean opponents of the war who say the US action has no moral basis. But he said opposition to the war on principle must give way to national interest.

"Many lawmakers and people are opposed to the dispatch of troops. The main reason is that this war had no grounds," said Roh.

"This is a logic based on both principles and reality. But regretfully, international politics are swayed by the power of reality, not by principles."

Opinion polls show some 80 percent of South Koreans oppose the war while North Korea has condemned Roh's planned troop dispatch as a "criminal act."

Communist North Korea fought against the United States and South Korea during the 1950-53 Korean War and hostilities have technically never ended.

The war finished with an armistice, rather than a peace treaty, and US and South Korean troops are separated from North Korea's 1.1 million-strong army by the world's most heavily fortified frontier.

WAR.WIRE