Cuban President Fidel Castro said here today that "not a single Cuban" is involved in the current fighting in Zaire's southern Shaba Province, and denied any involvement by his country in the arming or training of the invaders operating there.

"I want to assure you that there is not a single Cuban involved," Castro said at a news conference shortly before leaving for Mozambique, where he met later with President Samora Machel. "We have nothing to do with it all and we have not equipped nor trained the forces which are fighting the ruling clique in Zaire."

Castro also spelled out in some detail for the first time his attitude toward Cuba's involvement in the nationalist struggle in southern Africa, indicating that there are limits to its capabilities and that the "front-line Black African states would play a determining role in deciding what the Cubans would do.

Zaire President Mobutu Sese Seko has strongly implied in statements to the press since the fighting began two weeks ago that Cubans were involved in the Shaba fighting. He apparently regards the trouble there as Cuban-backed invasion of hostile forces from neighboring Angola.

The insurgents are thought to consist mostly of troops who supported the secessionist movement led by the late Moise Tshombe in the early 1960s in Shaba, then known as Katanga Province. Several thousand Katangan soldiers fled into Angola when the separatist effort collapsed.

These Katangans later fought for the Soviet and Cuban-backed Popular Movement for the Liberation of Angola, which emerged victorious in the Angolan civil war last year over Zaire-backed factions.

Castro said that Cuba regarded the fighting as an "internal problem" of Zaire, and added "as far as we are aware" Anola has not been involved either. He said, however, that Angola had been the victim of "acts of agression" from Zaire in complicity with "the forces of imperialism."

He charged that Mobutu was taking advantage of the situation to obtain more military aid for "Yankee imperialist" and "European neocolonilists."

Regarding the African nationalist struggle in white-ruled countries of southern Africa, Castro said, "independence is not brought from abroad" and must be "primarily the concern of the Africans themselves."

Cuban assistance is reported to consist now of several hundred instructors helping to train African nationalist guerrillas of white-ruled Rhodesia in camps here and in Mozambique.

Asked about the possibility of detente between Cuba and the United States, Castro repeated his conditions that Washington must first cease its hostile attitude toward his country and lift its trade embargo.

Castro came here on short notice from Ethiopia Thursday and left on the eve of Podgorny's arrival.

There are about 50 Cuban doctors and other technicians serving in Tanzania, and Cuba is helping to build three agricultural schools there.