THE NAGGING question of American economic ties with apartheid has reached the District Building in the form of a bill offered by council member John Ray to ban city pension investments in banks and corporations that do business in South Africa. We respect the concern propelling Mr. Ray's "disinvestment" initiative, but we oppose it on practical grounds.

A persuasive analysis of disinvestment was made in the 1981 Rockefeller Foundation report, "South Africa: Time Running Out," led by Ford Foundation president Franklin Thomas. It reviewed the arguments in favor of disinvestment (that U.S. corporations bolster the white-minority South African government, that the flow of foreign capital has not improved conditions for blacks, that the pro-disinvestment inclinations of black South Africans should be respected); and it reviewed the arguments against (that other Western nations would fill the gap left by American disinvestment, that disinvestment might not improve conditions for blacks either, that foreign capital gives blacks jobs and other trickle-down benefits).

"Having considered both sides of the argument," the commission said, "we conclude that there is not much of a choice." Other nations' corporations would fill an American gap. Even if they too withdrew, change would be uncertain. Meanwhile, foreign companies bring "tangible benefits" to some blacks. Many South African blacks, the commission suggested, favor disinvestment "because they do not believe U.S. corporations are sufficiently committed to change." Rather than disinvest, the corporations should stop expanding, spend more on social development, and promote the fair-employment procedures embodied in the "Sullivan Principles."

Few who are familiar with the repressive essence, the moral ugliness and the durability of apartheid will fail to feel tugged to strike at it. But the likely effects of any given tactic or gesture must be calibrated. American corporations profit under apartheid, but they also give some blacks a livelihood, training, promotions. White South Africa gains something, yes--but, importantly, non-white South Africa gains too.

As for the threat of Rep. Stanford Parris (R-Va.) to overturn the legislation if the District approves the "unwise" Ray bill, it represents a callous approach to the tragedy of apartheid and a slap at District home rule. We hope the council will not let his provocative intervention ruffle its study of the bill.