A senior Reagan administration policymaker will travel to Africa next month to test the waters for a new U.S. policy toward the region, the White House announced yesterday.

The mission of Chester A. Crocker, who has been nominated to be assistant secretary of state for African affairs, is expected to include black Africa "front-line" states such as Angola, Mozambique and Zimbanwe as well as South Africa and Nigeria, according to State Department officials. w

The Crocker trip, coming after the completion of "the initial phase" of a U.S. policy review toward the continent, is intended to broaden the new administration's consultations with Africa and sketch the outlines of emerging positions, officials said.

The White House statement said the "broad objective" of the United States is "to strengthen the security of southern Africa, a region of growing importance to our interests."

In this connection, "the United States strongly supports negotiated solutions to the problems of the region," the statement said. The U.S. aim of "a genuinely independent and democratic Namibia, recognized by the international community," was specifically mentioned. "To this end, we will work with all interested parties," the statement said.

In a reference to East-West conflict, the statement said "the path of violence serves no one's interest except that of our global adversary."

The United States is seeking to strengthen communications and understanding with "all Africa states," according to the White House statement. This evidently includes South Africa, where the Reagan administration has been taking a less hostile line than the Carter administration did.

"There can be no question of American support for apartheid, which is repugnant to our multiracial and democratic society," the statement said. It added, "We intend to make our views plainly known, not in a spirit of confrontation but of constructive help."

The statement did not mention the administration's request that Congress repeal the Clark amendment banning covert or overt U.S. aid to rebel forces in Angola.

However, Lannon Walker, acting assistant secretary of state for African affairs pending Crocker's confirmation, defended this move as a matter of principle. He did so under fire yesterday before the House Foreign Affairs subcommittee on Africa.

Walker's testimony stressed the "strategic, economic and political importance" of southern Africa to the United States. He said the area "contains a wide range of developed and undeveloped mineral and energy resources.

Regarding South Africa, Walker said, "We believe that it is the task of the western world to encourage purposeful, evolutionary change."