The race for D.C. delegate to Congress has acquired an issue other than Democrat Eleanor Holmes Norton's taxes: a 1985 letter in which Republican Harry M. Singleton opposed the efforts of "so-called black leaders" to force American businesses out of South Africa to protest apartheid.

Several anti-apartheid groups are expected to hold a news conference today to denounce Singleton for the letter, which he wrote to The Wall Street Journal while serving as the assistant secretary of education for civil rights in the Reagan administration.

In it, Singleton suggested that a withdrawal of U.S. firms would be useless because other nations would fill the market gap and because the "real losers" would be black South Africans who would "lose jobs as well as great allies in American corporations which have brought about dramatic changes on their own in South Africa." He said disinvestment was a "craze" advocated by "so-called black leaders . . . out of step with the times."

At that time, Reagan faced mounting pressure for sanctions against South Africa, a campaign that began with demonstrations outside its embassy here and led to the Comprehensive Anti-Apartheid Act of 1986 limiting imports from South Africa and ending new U.S. loans and investment there. Those sanctions remain in effect, supported by anti-apartheid leaders Nelson Mandela and Bishop Desmond Tutu.

Noting the involvement of "thousands" of D.C. residents in the South African protests, four anti-apartheid groups said in a statement prepared for the news conference today that they were "gravely concerned" about Singleton's letter and linked it to his service as an assistant secretary of education.

"Singleton's stand on South Africa, coupled with his failure to enforce civil rights policies during his tenure with the Reagan administration, raises serious doubts about his ability to advocate on our behalf," said the four groups. "Mr. Singleton charged that advocates of divestment and sanctions were 'out of step with the times.' We say Harry Singleton is out of step with the people of D.C."

The groups -- the Washington Office on Africa, the Africa and Diaspora Committee of St. Augustine Church, South Africa Women's Day Committee and the Southern Africa Support Project -- called upon Singleton to "publicly clarify" his position.

In an interview, Singleton said he supported sanctions and divestment then and now. He wrote the letter, which he signed only with his name and not his government title, to illustrate the pitfalls of a "unilateral" withdrawal from South Africa by U.S. companies, he said.

Singleton, who said he had no regrets about sending the letter, said it was "really a non-issue" raised by Norton as an "act of desperation to try to salvage their sinking campaign."

He added that there were more people "upset with her failure to do what she is supposed to do," a reference to the failure of Norton and her husband, Edward, to file D.C. income-tax returns for the past seven years.

Asked about Singleton's explanation that he did not want the United States to act alone, Aubrey McCutcheon III, of the Washington Office on Africa, said that in 1985, anti-apartheid groups had wanted the United States to be a leader in the sanctions movement, and therefore he did not accept Singleton's position.

Norton, who was once arrested during an anti-apartheid demonstration outside the South African Embassy, said it was "unthinkable" that the District would elect "someone who opposed sanctions and disinvestment, about which there is virtual consensus in this city."