Durban, South Africa — President Mugabe’s party was expected to sign an agreement with the main opposition in Zimbabwe yesterday paving the way for substantive talks on ending the country’s political crisis, officials from both sides say.

President Mbeki of South Africa was to witness yesterday’s signing in the Zimbabwean capital, Harare, according to the officials, one a member of the decision-making council of Mr. Mugabe’s Zimbabwe African National Union-Patriotic Front. The second is from the opposition Movement for Democratic Change’s national executive. Both asked not to be identified.

The memorandum of understanding to start full-scale negotiations was expected to be signed after the two sides made progress in talks last week in South Africa, one of the officials said. The accord sets out the way in which the discussions between the two sides will be conducted, he said.

Mr. Mugabe claimed victory in a presidential runoff election on June 27, extending his 28-year rule of the southern African nation. The MDC leader, Morgan Tsvangirai, withdrew from the poll in protest at what he said was a state-sponsored campaign of violence against his supporters. The United Nations, America, and European countries consider Mr. Mugabe’s government illegitimate.

The MDC has said political violence must end and an estimated 1,500 political prisoners must be freed before talks commence. The party says at least 115 of its supporters have been killed by state security forces and youth militias since a first round of elections in March.

Mr. Mbeki was mandated by the 14-nation Southern African Development Community to mediate an end to the political crisis in Zimbabwe. The African Union has urged Messrs. Mugabe and Tsvangirai to form a government of national unity.