The leader of South Africa’s governing National Party said that the outlawed African National Congress could become a partner in political negotiations if it commits itself to the “pursuit of peaceful solutions” to the country’s racial conflict. Frederik W. de Klerk, who is likely to become president after the Sept. 6 parliamentary elections, urged the ANC to follow the lead taken by its imprisoned leader, Nelson R. Mandela, who met earlier this month with President Pieter W. Botha. “The ball is now squarely in the court of the ANC. . . ,” De Klerk told a Cape province party convention. It was Pretoria’s most straightforward offer yet to the exiled guerrilla movement to include it in direct talks.