Thousands of baton-wielding police blocked an anti-government rally Thursday after authorities, stung by the deaths of six riot police, warned they would take emergency measures to halt violent protests.

About 8,000 riot police blanketed the downtown area in a major show of strength to block a rally called by striking workers and dissidents to denounce the government of President Roh Tae-woo.Squads of policemen in green combat fatigues, visored helmets and armed with shields and nightsticks patrolled the streets, dispersing onlookers and keeping the area clear.

Police vehicles roamed the streets and squads of troopers were positioned at every major intersection.

Dissident leaders had said that up to 50,000 workers and students would take part in a major rally in this industrial port city 120 miles southeast of Seoul.

But dissident leaders said the enormous display of police strength had frightened workers, and no one was prepared to come onto the streets.

"How can we march for our rights when there are so many police?" said one dissident leader.

There were no signs of protests in the city. Police said about 9,000 workers dispersed voluntarily after holding peaceful rallies at their factories.

Police arrested about 250 workers and students who tried to attend the scheduled rally.

"They talk big, but they don't dare come out," said a grinning riot police officer.

Many of the riot troopers wore black mourning ribbons for their comrades who were killed early Wednesday in the nearby city of Pusan during a raid on a college to rescue five police officers being held hostage by radical students.

Roh warned later Wednesday that he would invoke emergency powers to halt a wave of violent anti-government protests and strikes that have hit South Korea in recent months.

The police deaths shocked South Koreans and brought calls from government and opposition leaders for an end to violent protests. It was the worst loss of life in political violence since a 1980 anti-government uprising in Kwangju left at least 192 people dead.

Police said Thursday that they would charge five student leaders with murder and arson, charges that could be punishable by death. Police said lesser charges would be filed against 40 other students.

Also Thursday, the governing and opposition parties agreed to enact a law against firebombs. Prime Minister Kang Young-hoon said the proposed law should require disclosure by heads of universities, churches and temples of the existence of firebombs on their premises.

The Education Ministry was given authority to request police intervention in putting down campus unrest. Currently, it's up to the school to ask for police assistance.

In Seoul, hundreds of radical students shouting "Down with the Roh regime" marched on at least three campuses. But students avoided clashes with riot police stationed outside.