Cuban President Fidel Castro and Joshua Nkomo, a guerrilla leader fighting the Rhodesian government, charged in separate television interviews yesterday that the Central Intelligence Agency has continued to interfere in Angolan affairs in violation of congressional restrictions outlawing such involvement.

"We know from very good sources that recently the CIA established contact with UNITA in Angola and ... promised U.S. assistance," Castro said on "Issues and Answers" (ABC, WJLA).

He claimed the assistance to UNITA, the pro-Western United Front for the Total Liberation of Angola, "constitutes a very serious involvement in Angola's interior affairs."

Nkomo, speaking on "Face the Nation" (CBS, WTOP), said his information about U.S. "assistance" to UNITA's fight against Angola's Marxist central government came from "those who know."

These sources say they "believe (UNITA) Angolan forces ... do not get some aid from the United States" by way of South Africa, Nkomo said. "I have no reason to believe that the CIA is not aiding South Africa to aid some dissidents in Angola to overthrow the government (because) the United States has not recognized the legitimate government of Angola."

In 1976 Congress approved an amendment by Sen. Dick Clark (D-Iowa) prohibiting U.S. involvement in Angola. But Carter administration officials reportedly have been studying the possibility of seeking repeal of the amendment to enable the United States, through a third party, to provide aid to UNITA.

Clark has strongly opposed that idea.

For his part, Castro insisted that the United States presently is interfering in Angola's domestic policy by working with UNITA. "I declare it so, in a fully responsible way. We know that from very good sources," he said without elaboration.

His charges were the latest in a frequently loud, often confusing media war between himself and President Carter.

Carter has accused the Cuban president of working in tandem with the Soviet Union to stir unrest on the African continent, and of aiding and abetting the Katangan rebels who invaded Zaire last month. Castro, as he did in the interview aired yesterday, has repeatedly and passionately denied these charges.