JOHANNESBURG, JUNE 15 -- The union for most black Ford workers reacted warily today to a company offer of a 24 percent share in its South African company, which the union said was only "marginally profitable."

Spencer Stirling, managing director of the South African Motor Corp., owned by Ford and Anglo American Corp., said its proposal to the National Union of Metal Workers was "the best deal in history."

Ford has offered to give more than half its 42 percent interest in South African Motor Corp. to the 4,500 workers in the form of a trust and sell the rest to Anglo American.

The arrangement would allow Ford to shed its investment in South Africa, protect the interests of its workers -- 70 percent of whom are black -- and continue to market its products in this country, a Ford spokesman said in Detroit.

Union spokesman Charles Mthiti said hesitancy about the offer arose "because people need to have a guarantee of how much would that 24 percent equity be and how it would benefit them in future.

"We are looking at a company which for some time has been unprofitable and if it would be that their equity would not pay out anything in future then obviously the workers here would not benefit anything," he said. "It would just be an empty agreement."

Mthiti said the union's main demand was job security. He said Ford should guarantee severance payments to those who lose their jobs as a result of its action. He also said Ford should guarantee that the workers at South African Motor Corp. continue to receive the benefits they are now getting.

Demands for job security and severance pay also were made of General Motors last year when it turned over its Port Elizabeth plant to local management. The auto workers went on a protracted strike in the weeks before Christmas. Many lost their jobs and the U.S. firm pulled out without meeting the demands.