GRAND RAPIDS, Mich. (AP) _ Delegates to the Christian Reformed Church's annual synod capped a three- day debate by extending its relationship with a South African church to give it time to reconsider its support of apartheid.

''We have considered this a tremendously important issue and don't think the answer, right now, is to sever ties,'' said the Rev. Clarence Boomsma, a member of the church committee which studied the apartheid issue. He was a prime supporter of the plan to give the Reformed Church of South Africa four years to re-evaluate its support of apartheid.

''We'll now wait until 1989 to see if (the Reformed Church of South Africa) changes its policies,'' he said. ''If it doesn't change by then, I'd be willing to throw in the towel.''

Apartheid is a policy which separates the white minority from the majority of blacks in South Africa. The CRC last year declared apartheid a sin and theological justification of it heresy.

A member of a smaller Dutch Reformed denomination in South Africa denounced Tuesday's decision.

''I'm disappointed,'' said Daniel Cloete, a New Testament scholar and member of the Dutch Reformed Mission Church in South Africa. ''My people back home will interpret this as support for apartheid.''

Cloete accused the synod's 160 delegates of ''backing off on your commitment to fight racism'' and said his church would reconsider its position with the CRC.

Victor D'Assonville, representing the Reformed Church of South Africa, said he was happy with the decision to maintain relations.

''We are living in apocalyptic times in South Africa,'' he said. ''God is forcing us as Christians to link hands firmly. We need one another. We shouldn't be apart.''

The Reformed Church of South Africa has 400 churches and more than 155,000 members, about 20 percent of whom are black or colored.

The Dutch Reformed Mission Church, which has ties to the CRC, is a spinoff of the predominantly white Dutch Reformed Church, the largest reformed denomination in South Africa.

The CRC, with more than 300,000 members in the United States and Canada, does not have ties with the Dutch Reformed Church.