The anti-apartheid African National Congress Saturday opened its first two legal congresses in South Africa in 31 years and a keynote speaker accused Pretoria of fomenting a wave of factional black violence.

ANC Treasurer-General Thomas Nkobi told the Cape Town regional meeting, attended near the city by some 500 delegates of 81 branches, the government had a dual agenda - "to negotiate with the ANC for the purposes of responding to international pressure" and to promote the bloody violence "in order to weaken the ANC."ANC Internal Leader Walter Sisulu made a less hardline speech at the Johannesburg-area Congress of about 400 delegates from some 90 branches, but said, "The period we find ourselves in is ripe for the transfer of power to the people," and added, "The ANC must play a leading role."

"It is this double agenda which is designed to break us down," charged Nkobi, a member of the ANC's 37-member National Executive Committee. "They are using every vile tactic possible to weaken our movement.

"The vicious violence . . . is aimed at destroying our spirit of resistance and defiance," he told representatives of some 40,000 ANC members in the Cape Town area, apparently referring to allegations of police involvement in stirring the strife.

Nkobi's tough stance contrasted with more cautious statements of recent weeks from ANC leader Nelson Mandela, who has never accused the government of outright and deliberate duplicity.

Sisulu also did not pin the township battles directly on the government, but he did say "suspicious elements are involved."

The congresses are due to make formal statements and possibly recommendations on responses to charges of government involvement in the now-dormant violence when they end Sunday.

President Frederik de Klerk imposed a tough set of military-style measures codenamed "Iron Fist" this month to quell the fighting, which in more than six weeks killed up to 800 people.

De Klerk has repeatedly denied the government wants to gain any advantage from the strife.