The D.C. City Council yesterday tentatively approved a bill prohibiting city investments in corporations doing business with South Africa, ignoring strong warnings from Capitol Hill that passage of the measure could open up a Pandora's box of controversy over home rule itself.

If the bill becomes law, it would require the city's retirement board to sell $63.5 million in common stocks in 31 companies that have dealings with South Africa, and the District would have to remove several million dollars from accounts at American Security and Riggs National banks, according to council figures.

The bill is intended to withdraw any indirect financial support to South Africa's apartheid policy.

The measure was passed by voice vote with no discussion on the first legislative session of City Council after its summer recess. It is scheduled for final passage Sept. 20.

This would be too late for the legislation to go into effect this year, Hill staff aides said, because all District bills must undergo a congressional review period of 30 legislative days--days in which at least one house of Congress is in session.

With the House planning to adjourn on Oct. 26, only bills that get to Congress by Sept. 19 could get through the review period unless the adjournment date is delayed, the aides said.

But it would not be too late for congressional opponents of the South Africa bill to get a disapproval measure considered this year, and congressional aides predicted there is a good chance that such a disapproval effort would succeed.

At the same time, Hill experts think a battle over the bill would lead to a far more sweeping debate over Congress' method of disapproving D.C. bills and over the validity of home rule itself. This is a result of a recent Supreme Court ruling knocking down the legislative veto mechanism, which is used in more than 200 laws including Home Rule.

Congressional and legal experts still are unsure how the Supreme Court ruling applies to home rule, and they are quietly trying to figure out a way to amend the Home Rule Act to make sure it complies with the requirements outlined in the ruling. This would include action by both houses of Congress and the president to disapprove any D.C. law. Under current procedures, some laws may be disapproved by a vote of only one House.

In the meantime, consideration of the controversial South Africa bill could lead to court suits either by opponents questioning the validity of home rule and therefore of the bill, or by proponents if the measure is overturned using the current procedures. Either way, the issue of home rule itself could be thrown into the courts where the outcome is highly uncertain.

"It will be a mess," concluded John Gnorski, minority counsel of the House District Committee. If the bill is sent up, friends of the District on both sides of the Hill probably will scramble to try to amend the Home Rule Act before a disapproval resolution could be considered, he said.

The bill's sponsor, council member John Ray (D-at large), dismisses the congressional concern as "rather a silly argument" not warranting any delays in passing the legislation and sending it to Congress. There are other controversial measures on the books that opponents could sue over, he said.

"If they are going to challenge it, let them do it and see how it turns out," he said.

Mayor Marion Barry's administration testified in support of the measure. The mayor's spokeswoman, Annette Samuels, said yesterday that Barry would have no comment on whether the bill should be delayed because of congressional concerns.