JOHANNESBURG, FEB. 8 -- African National Congress leader Nelson Mandela threatened today to unleash a wave of "mass action" aimed at making new investment here impossible if the United States and European nations lift sanctions against South Africa.

It was the first time the ANC has hinted at using such tactics against foreign companies.

Speaking at a news conference, Mandela said he was sure President Bush would be "keen" to consult with the ANC before making any decision on easing sanctions in response to President Frederik W. de Klerk's announcement a week ago that he will ask Parliament to repeal three basic apartheid laws.

Mandela said he had "no doubt" that Bush would not proceed the same way the European Community did Monday, when its 12 foreign ministers announced that their governments would lift sanctions once the repeal takes effect. Bush so far has followed "very correct procedures" in dealing with the ANC, even briefing him by telephone on de Klerk's visit to Washington last September, the ANC leader said.

Mandela said European governments had made "a very serious mistake" and "error of judgment" in announcing their decision before consulting with the ANC. He accused them of wanting South Africa "to be turned upside down" with protests by deciding to lift their last economic sanctions, a ban on the import of South African iron, steel and gold coins.

"You can expect that mass action in this country is going to be the order of the day and that the situation in the country is going to be so unstable that no wise businessman is going to want to invest in this country," he warned.

The term "mass action" refers to the current ANC campaign to press for its reform demands through street demonstrations, mass rallies, boycotts and other forms of protest. The government has denounced the campaign as contrary to the ANC's commitment to end its armed struggle and enter peaceful negotiations for a new constitution.

Later in his news conference, Mandela denied he was making any "threat" against the European Community and expressed confidence it would change its mind once it had heard the ANC's "strong case" against lifting sanctions. He said a joint delegation of representatives from the ANC and its rival, the Pan Africanist Congress, would go to Europe to present their argument against any changes now.

The ANC leader conceded there was a contradiction between his expressions of concern about the deteriorating economic situation here and his opposition to ending the sanctions that are generally acknowledged to have contributed to the problem.

But he said sanctions were "one of our principal weapons of peace" that the ANC could use to induce the government to make fundamental reforms. "This is the price we are prepared to pay in order to determine our affairs, in order to get the vote, in order to sit in Parliament," he said.

Meanwhile, the ANC's department of arts and culture said it was not relaxing its boycott of "apartheid cultural organizations" by agreeing to allow various international artists to perform here. It said the ANC would give priority to groups and individuals who had supported the struggle against the apartheid system of racial separation, but would also consider "those who meet the criteria for coming to South Africa." It did not elaborate.