INTERNAL anti-apartheid leaders, long sidelined by the exile leadership of the African National Congress, appear set to take control of the organization at its landmark national conference that begins here today.The ascendancy of talented trade unionists and other internal activists will both democratize and radicalize the ANC, but could also boost the faltering momentum toward formal negotiations with the government. "Until now the government has consistently outmaneuvered the ANC in the vital area of strategy and tactics," an ANC official concedes. "We need to return to a leadership style which allows greater consultation with the grass-roots." The five-day conference, the first of its kind held inside the country since 1959, is the most talked about political event in South Africa since President Frederik de Klerk legalized the ANC and freed Nelson Mandela 17 months ago. Mr. Mandela is assured of being elected ANC president when the ailing Oliver Tambo steps down during the conference. Mr. Tambo is likely to be retained as honorary president. The government, which concedes that grassroots militancy within the ANC has slowed the negotiations, is watching developments closely. "I believe the ANC conference will help the process of political negotiations," says Deputy Constitutional Development Minister Roelf Meyer. "The gap between us and the ANC is not as wide as it seems." At the meeting, the ANC will discuss a draft constitution for South Africa based on a multi-party democracy, with an independent judiciary, a Bill of Rights, and a constitutional court. A central task the ANC faces is to integrate its old-guard membership - often considered high-handed and undemocratic - with internal leaders well-schooled in strategy and tactics. "What we are facing is the challenge to merge the various organizations, structures, and styles of the ANC into a new organization," says Mandela adviser Frene Ginwala. "The events of the past year or so demand a new organization. In exile we were primarily a military organization. We were authoritarian." Nominations for the 55 elected positions on the proposed 90-member executive indicate that more than half the current leaders could be swept aside by younger internal leaders and former prisoners in the first democratic elections in more than three decades. Regional nominations indicate the ANC is trying to avoid a power struggle for the key post of deputy president by nominating its respected internal leader, Walter Sisulu, for the job. International department head Thabo Mbeki, a skillful negotiator and diplomat, had been seen as the front-runner for the post in a contest with the ANC's fiery military chief of staff, Chris Hani. But the nomination of another key moderate for the deputy president slot, the ANC's Zulu intelligence chief, Jacob Zuma, could split the moderate vote. Mr. Zuma is seen as a contender for the third-ranking post of secretary-general, but the respected miners' leader, Cyril Ramaphosa, is tipped as the favorite fo r this job. A key pointer to the mood of the conference will be the fortunes of the ANC's other top-ranking Zulu, Harry Gwala, a hard-liner from Natal province. Mr. Gwala and Zuma represent opposite poles within the ANC, and victory for Gwala could mean escalating conflict between the ANC and Chief Mangosuthu Buthelezi's Inkatha Freedom Party, the ANC's main rival. ANC officials say the main challenge of the conference is to assess the current situation and Mr. de Klerk's true intentions. This debate will dwell on the role of the security forces in the violence and De Klerk's apparent reluctance to do what is needed to end the carnage. The conference outcome is expected to determine the pace of negotiations and of the ANC's transformation from a broad liberation movement to a more flexible political party. There is a growing acceptance within the ANC that there is no alternative to negotiations. "Those of us who had doubts are behind negotiation now," says Linda Shope Mafole, an executive member of the militant ANC Youth League. Yet the divide is growing between those prepared to share power with the ruling National Party and its allies and those who want to hold out for total power in the first post-apartheid government. The South African Communist Party - the ANC's ally - and the ANC's military wing, Umkhonto we Sizwe, are the most vocal advocates of the hard-line position. The hero of the ANC underground, Ronnie Kasrils, believes negotiations will make progress only if backed up by popular protests. "I think the main factor now should be mass action," he says. "I would like to see the ANC bringing hundreds and thousands of people into the streets in support of its demands. ... to bring the country to a standstill." A main policy issue will be to spell out a new position on sanctions. At the ANC conference last December, militants thwarted efforts by the leadership to adopt a more realistic stance. Another key decision is to define the shape of an interim administration. De Klerk rejects the ANC demand for a sovereign interim government, but concedes that "transitional mechanisms" must be negotiated to bring representative black leaders into the government. He also rejects the ANC demand for an elected constituent assembly as the body to draw up the new constitution on the grounds that an election now would spark violence and establish straight majority rule as the model before talks begin.