President Roh Tae-woo announced Monday that he is postponing a national referendum on his performance - a campaign promise - and claimed leftist forces are trying to overthrow the government.

In a nationally televised address, Roh said the nation faces a major threat from radical groups and that going ahead with the referendum now would risk plunging South Korea into new chaos."Violent leftist forces are trying to overthrow the government," he said.

The former general said the referendum would be held sometime in the future but gave no indication of when or how. Roh had been expected to announce this week that the referendum would be held about April 12.

It was not clear if Roh was backing away from the referendum because of concern about potential unrest or because he feared the government could not win the vote and might be forced into new elections. Some government officials had expressed concern about Roh's ability to win a referendum.

The government had said earlier that Roh would not resign if he was defeated, but some administration officials conceded a defeat would put pressure on Roh to call elections.

Critics said Roh could not win a referendum. Roh said on television that "it would not be of help to the country to hold a national referendum for my performance in office at this juncture."

The main opposition parties said they accepted Roh's decision but would watch to ensure the government does not attempt to retreat on any other promises to bring in full democracy.

"We feel sorry for the people to have such a president who has unilaterally postponed the referendum without presenting a concrete alternative," said the Reunification Democratic Party, one of the two main opposition groups.

Dissident groups denounced Roh's decision, saying it proved the government never intended to hold a referendum and proved that the administration knew it could not win a popular vote.

The United National Democratic Movement, the nation's main dissident alliance, said it would proceed with plans to campaign for Roh's ouster.

"Roh's postponement of the referendum is an act deceiving the people," the alliance said.

Several hundred radical students shouting "Punish Roh Tae-woo" attacked two police stations with firebombs Monday in Kwangju, the South Korean news agency Yonhap reported. No arrests or injuries were reported.

Radicals have organized a series of violent anti-government protests, but they lack broad support.