ARUSHA, TANZANIA, DEC. 4 -- The international antiapartheid movement vowed today to intensify its pressure for stronger economic sanctions in order to isolate South Africa further from the world community.

At the first international conference organized by the 75-year-old African National Congress, the main guerrilla force battling white minority rule by Pretoria, 500 delegates from more than 40 countries called on governments and private organizations to step up demands for more sanctions and cultural and academic boycotts.

At the end of the four-day meeting, the antiapartheid campaigners declared that South Africa should be denied financial assistance and that pressure should be exerted on the International Monetary Fund to sever its links to the Pretoria government.

The delegates also called for an internationally coordinated campaign of action against corporations that circumvent existing sanctions and disinvestment measures.

ANC President Oliver Tambo, in closing the conference, said that blacks have reached a "watershed in the history of our struggle" because there have been increasing signs that South Africa's apartheid policy of racial separation is beginning to crumble.

Tambo pledged that while these sanctions and boycott campaigns were being intensified by supporters of the ANC, the guerrilla organization would "raise the armed struggle to new heights and respond in a militant manner to the terrorism of the state."

There was no hint of divisions among the delegates over the issue of sanctions, as there have been inside South Africa between militant and moderate blacks and among some members of the liberal opposition in Parliament.

The conference did reflect differences over sensitive cultural boycotts. In the end, the group issued a statement simply calling on the ANC to consult further with antiapartheid groups inside and outside of South Africa to establish "criteria and mechanisms to continue the intensification" of such measures.