Pretoria — Thousands of people protesting the high cost of AIDS medications marched on the U.S. Embassy on Monday while manufacturers asked a judge to throw out a law activists say is needed to get AIDS drugs to the poor.

The demonstrators in Pretoria, South Africa's capital, want the United States to pressure drug companies to withdraw a lawsuit they filed to overturn a law that gives the South Africa's Health Minister a limited right to import generic versions of patented drugs or licence their domestic production. Smaller protests were also held in Cape Town and the east coast city of Durban.

More than three dozen pharmaceutical companies opened their lawsuit in the Pretoria High Court on Monday by arguing that a 1997 amendment gave South Africa's Health Minister the power to arbitrarily ignore patents and trample the rights of drug companies.

South African officials maintain the law is needed to save those who cannot afford expensive AIDS treatments.

AIDS activists have said the outcome of the case will determine whether developing countries are allowed access to cheap, generic versions of AIDS medications.

The disputed law, which has never been used, allows the Health Minister "in certain circumstances so as to protect the health of the public" to set conditions for the supply of more affordable medications.

Stephanus Cilliers, a lawyer for the pharmaceutical industry, argued the law could be used to import patented medicines from other countries, where they are cheaper, hurting the local patent holder and damaging the industry's international pricing system.

He said the government recently signed the Trade Related Intellectual Property Agreement, the treaty administered by the World Trade Organization that governs international patent rights.

"We can hardly be seen now to breach this treaty with respect to medicine," he said.

Mark Hayward, a lawyer who represents AIDS activists, said the pharmaceutical industry had unfairly assumed the law would be interpreted to destroy their patent rights. But the government has gone to great lengths to court foreign investment and would not likely endanger that by infringing on patents, he said.

"They are making big presumptions before they see the regulations to go with the act," he said.

More than 25 million of the 36 million people infected with HIV, the virus that causes AIDS, live in sub-Saharan Africa, one of the world's most impoverished regions.

"There can be no better world whilst people in developing countries are dying from curable diseases just because these drugs are so expensive," Blade Nzimande, secretary-general of the South African Communist party, told the protesters in Pretoria.

Glenys Kinnock, a British member of the European Parliament, told the protesters South Africa was "suffering an apartheid of drugs."

When the law was passed, the United States government vehemently opposed it, going so far as to threaten trade sanctions against South Africa.

As then-vice president Al Gore began campaigning for the presidency, however, protesters began publicly embarrassing him by bringing up the issue. In 1999, the Clinton administration changed its position, agreeing to support South Africa as long as the law was enforced in a way that did not conflict with international trade agreements.

President George W. Bush's administration reaffirmed that policy.

"The U.S. government is actively engaged in co-operative efforts to assist developing countries to confront the HIV epidemic including by providing access to affordable medicines," said Valerie Crites, spokeswoman for the U.S. embassy in Pretoria.

The hearing in the Pretoria High Court was expected to last more than a week and the ruling might not come before the end of the year.