Churches in the United States "have a tremendous potential" to influence the elimination of apartheid in South Africa and the eventual development of a multiracial society there, said a South African churchman who has devoted his life to those goals.

"I am very grateful for what the {American} churches have done" in launching the economic boycott movement, the Rev. C.F. Beyers Naude said in an interview here this week.

But he would like to see American churches lean harder on the Reagan administration to pressure the South African government to change.

And he encourages American churches to "offer moral and financial support to thousands of young blacks" in South Africa to come to the United States and study and prepare themselves for the inevitable time, he believes, when the black majority will take its place in running the country.

Naude, 72, was in Washington this week for the premiere of "The Cry of Reason," a documentary film that views the racial crisis in South Africa through his eyes.

It is a logical concept for a film, because Naude had a unique perspective on that battle.

Naude was born into the South African ruling class of Afrikaners, as the descendants of Dutch immigrants to the country three centuries ago are called. His very name echoes the history of their struggle for dominance in their adopted land. As chaplain to a famous general in the war of the Boers against the British at the turn of the century, Jozua Naude named his son for that national hero, Gen. Christiaan Frederick Beyers.

The son followed his father into the ministry of the Dutch Reformed Church and also into the Broederbond, an elite secret society that wielded strong influence in Afrikaner political and religious affairs.

Articulate and bright, the young Naude took his place as a rising leader in the church, where he was elected moderator of its largest synod. In the close mingling of religion and politics in South Africa, he was viewed by some as a possible prime minister.

But gradually, Naude's study of the Bible led him to the conviction that his church's support for apartheid was contrary to the scriptures. In 1963, when he founded the ecumenical Christian Institute to promote contact between black and white Christians, he was defrocked by his church.

In 1977, the government put the institute out of business and issued a banning order, a rigorous type of house arrest, against Naude. The order was not lifted until 1984.

"No reasons are ever given," either for the issuing or rescinding of the order, Naude said with a smile.

He said he was "just beginning to enjoy my freedom" after being released from the banning when he was asked to take over the leadership of the South African Council of Churches from Archbishop Desmond Tutu on Tutu's election as head of the Anglican communion in South Africa.

The council is virtually the only multiracial institution left in South Africa.

Naude agreed to stay for 2 1/2 years. "I thought it important in the South African situation that a black Christian take over that role," he said.

Earlier this year the Rev. Frank Chikane, a leader of the Apostolic Faith Mission and a former black consciousness follower of the late black leader Steve Biko, succeeded Naude at the SACC.

Now, "officially retired" from the SACC, Naude said he has turned down job offers because "I would like to use the period ahead of me -- whatever is left -- to write."

Although he was defrocked, Naude remained a member of the church of his fathers until 1980, when he moved his membership to the black branch of the Reformed Church in South Africa.

The final break was prompted by the white church's rejection in 1978 of an overture from the black church -- originally founded by African converts of the white church's missionaries -- to form a unified Reformed church in South Africa.

"They requested the white church to become united with them," and the whites refused, said Naude. "That was the reason for my leaving."

Despite its quasi-official status as the state religion of South Africa, the white church has cut itself off from most of the rest of Christendom over the apartheid issue.

It was expelled four years ago, in a highly emotional session, from the World Alliance of Reformed Churches, for its rejection of the latter's theological position that race discrimination is a sin.

Last year, said Naude, the white church took "the first hesitant step" toward the Alliance's position when it formally "admitted apartheid to be a mistake."

That caused a "clear schism," he said, with about 100,000 members favoring apartheid and 35 clergy pulling out to form the Afrikaner Protestant Church.

The departure of this far right wing could have "a positive outcome" for moderates in the white church who now can argue, "We've already lost this group so let's go ahead" with efforts to reestablish ties with other churches, especially other Reformed churches, Naude said.

Naude said he still may be too much "in the position of being anathema" to the white church to serve effectively in unity efforts.

"There is a real love-hate relationship there," he explained. "I have said there is no hatred in my heart. I have a deep sympathy for {the white church leaders}.

"If they accept my bona fides, they will come under criticism."

At the same time he is adamant in his belief that the white leaders "have to face the fact that ultimately South Africa will be an integrated society."

Without planning for such a future, he said, "you can't remain alive and {be} a meaningful church."