A British spokesman announced today that Lord Soames, the country's colonial governor pending election of an independent government, ordered Rhodesian security forces to stem guerrilla infiltration in violation of the 2-day-old cease-fire.

The spokesman said two guerrillas and a civilian had been killed by these forces. The cease-fire agreement banned cross-border movement by guerrillas still outside of Rhodesia.

The Rhodesian news agency said, meanwhile, that guerrillas ambushed and killed a white farmer and waylaid a busload of blacks in the eastern countryside.

On the political front, a representative of Robert Mugabe's wing of the Patriotic Front announced it has severed political ties with its guerrilla partners so that it can contest the forthcoming national elections on its own.

The go-it-alone plan was announced by Enos Nkala, chief local representative of Mugabe's Zimbabwe African National Unin. Nkala spoke to a crowd of 50,000 gathered for the first major rally staged by the local leaders of the Mugabe movement.

Informed of Nkala's remarks, Cephas Msipa, senior representative of Joshua Nkomo's Zimbabwe African People's Union, warned of the possibility of civil war between the black guerrilla movements, which had joined forces to fight for independence.