An anti-apartheid South, African diplomat and a U.S. official disagreed sharply last night over the issue of disinvestment by American companies at a forum at the John F. Kennedy Library in Dorchester.

Neo Numzana, acting chief of the African National Congress rebel group's non-voting delegation to the United Nations, called on U.S. businesses to pull out of the racist nation.

But State Department official William Jacobsen maintained that "The psychology of threatening disinvestment is more important than disinvestment because once you disinvest you have no more leverage" to change the country.

In its current position, American business not only supplies jobs for many Black South Africans, but it also spends $115 million to help improve conditions there through such means as academic scholarship, Jacobsen said. But he added that the U.S. plays a very small role in the economy, making up less than 2 percent of the South African gross national product.

Numzana said that the Blacks will not be hurt by the loss of American business and jobs.

"Those who've got jobs to lose have got slave labor to lose," Numzana said.