Prince George's County has banned purchases from companies that do business with South Africa, but county officials concede that does not mean Coca-Cola machines or IBM computers are going to be hauled out of county buildings any time soon.

Instead, county officials said yesterday, the package of antiapartheid legislation that the County Council passed Tuesday is unlikely to make a significant difference in the allocation of the county's $80 million annual purchasing budget.

The bills that the council enacted prohibit the county from buying from companies or depositing county money in banks that do business with South Africa. Two other nonbinding resolutions call for a review of the county's employe pension investment practices.

Exceptions included in the bills passed unanimously by the County Council allow "essential" purchases to be made from firms with South African ties if "no reasonable alternative to the purchase of the product exists; or the application of this [law] would significantly impair competition."

"The exceptions are important," said Ruth Webbon, the director of the county's Central Services Department, the division that oversees purchasing. "There is very little that could be hauled out, because most American corporations have investments in South Africa."

This means that the county's vehicle fleet, which includes Fords, Chryslers and General Motors cars and trucks, will not be affected. Nor is the county likely to stop buying IBM computers, Xerox copying machines and Nabisco crackers for its vending machines. All of those companies do business in South Africa, according to the Washington Office on Africa.

"Prince George's County isn't big enough to make significant impact on any one of these companies," Webbon said.

Some council members said it does not concern them that they have enacted a bill that may not be enforced. Council member Floyd Wilson, for example, said that local franchises of affected national firms that sell boycotted products should not be hurt by the law.

"I think basically the message we were trying to send was to national companies," he said, adding: "I don't see that any message we're sending will affect local companies We're not about to be putting people out of business here."

"Conveying the message is probably more important than the substantive effect," said Council Chairman William B. Amonett.

Curtailing county purchases in all South Africa-related firms, Amonett said, would "be a sacrifice I'm not sure everyone is willing to give."

If the bill becomes too much of a burden, Amonett said, it can be changed. "That's what repeals and modifications are all about."

But County Executive Parris Glendening said he will direct those responsible for enforcing the law "to make every effort" to meet both its intent and spirit.

Doug Tilton, legislative coordinator of the Washington Office on Africa, said that enforcement monitoring in such cases usually falls to local governments. Loopholes in the law, he said, are often "a compromise of sorts."

"Even getting it on the books is helpful whether it actually makes a difference or not," he said.