A City Council panel yesterday questioned whether the District has been sufficiently aggressive in making certain that the city complies with a law prohibiting the investment of public funds in banks and other financial institutions doing business in or with South Africa.

The law became effective in March.

During a briefing on efforts to implement the law, representatives from the office of the deputy mayor for finance presented the council's committee on consumer and regulatory affairs with a list of banks and financial institutions that have submitted affidavits indicating that they are not doing business with South Africa.

But City Council member John Ray (D-At-Large), sponsor of the South Africa legislation and chairman of the consumer committee, questioned whether some of the institutions are clear of ties with South Africa.

For example, Ray noted that six of the out-of-town companies on the list of those that submitted affidavits had outstanding South African loans totaling more than $2.5 billion, according to 1983 information provided by the United Nations Center Against Apartheid.

Ray said that the city needs to conduct spot checks and to be "creative" in seeking information to determine whether affidavits reflect the true picture of a company's financial status regarding South Africa.

William Kao, assistant treasurer for the city, told the council panel that it is not always possible for the city to verify information, especially when it may be contained in confidential documents.