President Roh Tae-woo, blaming "revolutionary forces" for the fiery deaths Wednesday of six policemen, said he would take emergency measures if social turmoil continued in South Korea.

The six policemen, all in their 20s, died of smoke inhalation or of injuries sustained while jumping from windows after student radicals set the nine-story library building ablaze at Dongui University in Pusan during a police raid."It has been made amply clear that behind the flames that divested those youths of their lives, there are forces bent on violent class revolution, believing in murder, arson, abduction and destruction," Roh said in a televised address Wednesday night.

State radio said the government had accepted the resignation of national police chief Cho Jong-suk, who took moral responsibility for the deaths at the university, where protesters had held five policemen hostage overnight.

The police chief in Pusan, South Korea's second-largest city, said two of the 11 officers hurt in the assault were in critical condition and not expected to live.

The president said: "Whether they be on campuses or at factories, violent revolutionary forces . . . will be chased to the end and punished according to law. They must be resolutely banished from this society."

He urged opposition parties and other critics not to accuse the government of repressing democracy when it was trying to crack down on lawlessness.

The national news agency Yonhap

said the president's speech did not rule out the possibility of martial law or other constitutional measures curbing basic rights.

The Pusan incident was by far the bloodiest in recent years in South Korea where violence on campuses and in strike-bound factories has become almost a daily feature.

A spokesman said Roh told an emergency meeting of key ministers the government could not tolerate challenges to its power.

Radical students captured five plainclothes police during an off-campus protest Tuesday in the southeast port city.

The demonstration had been called to protest police who fired more than 20 warning shots the previous night to beat back a radical student attack on a police post.

More than 600 riot police mounted a dawn raid on the campus Wednesday to free their colleagues, who were being held blindfolded on the seventh floor of the library building.

When police reached that floor, students set fire to barricades doused with gasoline. Trapped officers were either overcome by fumes or climbed out of the windows. Ten fell to the ground.