A group of black Seventh-day Adventists here is trying to use the denomination's worldwide general conference at the New Orleans Superdome next week to break up the church's racially separatist structures in South Africa.

Since early this year, Donald G. Morgan and his International Laymen Action Committee for Concerned Adventists have been importuning leaders of the 4.5 million-member church to repudiate the separate unions, as church organizational units are called, for South African Adventists.

"It is shocking and embarrassing that despite all the demonstrations and protests" -- a reference to the daily picketing and arrests outside the South African embassy by diverse groups -- "the Seventh-day Adventist Church has not taken a stand against apartheid," Morgan wrote church president Neal Wilson on Feb. l.

Morgan asked that church leaders deny recognition to delegates to the New Orleans convention from the white South Africa Union Conference. "To invite representatives from the white segregated [union]. . . constitutes a slap in the face of all who are opposed to apartheid," he wrote Wilson.

Morgan's letters and sporadic picketing by his group of the church's Takoma Park international headquarters during the spring brought no response from Wilson. So early this week he fired off a letter to New Orleans Mayor Ernest N. Morial, apprising him of the controversy involving the 2,300 church people about to descend on his city.

"Mayors are usually invited to address conventions, to welcome them," he explained, adding that he wanted to make sure Morial knew the facts before deciding whether to address the Adventists.

Morgan made three demands of Wilson: that the white South African delegation be banned from the conference; that Wilson state publicly that "the Adventist church is unequivocally opposed" to apartheid; and that church funds not be invested in companies doing business with South Africa.

Wilson is already in New Orleans for the conference, which opens next Thursday. But church spokesman Robert Nixon said "I don't think he will respond" to Morgan's demands.

He said the church's position is that "all properly appointed delegates will be seated. We are not going to deny a seat to a South African delegate because he or she is white."

According to Nixon, the white South African Union Conference has 18,851 members and the black South African Union Mission has 25,336. "Both unions, in theory, have said any church member can join any church he or she wants," he said, but acknowledged there is little interracial activity.

Although the New Orleans convention may adopt a resolution on race relations, he said, it will be couched in general terms. "If we go public on this it may be in the newspapers in South Africa."

Adventists, he said, "like to do anything by consensus" and seek to preserve "church unity. We are going in the direction of [integration] It may take us a while to get there, but when we get there it's going to be as a united church."