President Reagan's top adviser on Africa said yesterday there will be no "tilt or endorsement of apartheid" by the administration.

Chester Crocker, nominated as assistant secretary of state for African affairs, spoke to reporters at the airport on the fourth stop in a 10-nation tour.

Crocker said the goal of his trip is to "explore the trends of the Namibia question" and to formulate a new American policy on southern Africa. He said in Nairobi that the United States seeks a new relationship with South africa in a bid to lead it away from apartheid.

As Crocker arrived, Zimbabweans in both of the black-dominated political parties in the year-old coalition government here disclosed that top-level talks were under way on prospects of merging the parties into a powerful ruling bloc.

This disclosure was followed by the announcement of Andre Holland, a former junior minister in the pre-independence white-minority government of Ian Smith, that he was defecting from Smith's Rhodesian Front to form a new group.

The two main black parties are Prime Minister Robert Magabe's Zimbabwe African National Union, which draws its support from the majority Shona tribe, and the Zimbabwe African People's Union, party of minister without portfolio Joshua Nkomo and the minority Matabele tribe.