In an emotional declaration of defiance against black guerrillas, the foreign affairs minister of Rhodesia, Pieter van der Byl, pledged today to fight to the finish for every square inch of ground rather than surrender to "a loathsome and savage foe."

"The Russian colossus is on the march to subjugate and enslave all of Africa," van der Byl said in Inyanga, Rhodesia. He added that the United States and Britain are doing all they can to strangle Rhodesia politically and economically.

Meanwhile, Zambian President Kenneth Kaunda said in Lusaka that Rhodesian soldiers had exchanged gunfire with Zambian troops along the border between the two countries.

It was the latest in a series of border incidents since Kaunda declared last month that his country, which shelters black Rhodesian nationalist guerrillas, was in a state of war with its white-governed neighbor.

"Rebel troops fired to the Zambian side across the Victoria Falls Bridge and the Zambian troops returned fire immediately and silenced the rebel soldiers," Kaunda said.

Black African governments frequently use the term rebels to describe the white-minority Rhodesian leadership, which unilaterally declared independence from Britain in 1965. Victoria Falls, on the Zambezi River, is a major tourist site in western Rhodesia.

Rhodesia also reported the fighting, and both sides said they had incurred no casualties.