JOHANNESBURG, South Africa (AP) _ Hundreds of Johannesburg university students, many of them white, stayed out of class today to protest South Africa's military raids on three black- ruled neighboring countries, and 13 people were arrested.

In Zimbabwe, the foreign ministers of six countries bordering South Africa met to discuss the attacks on the capitals of Zimbabwe, Botswana and and Zambia in which at least three people were killed and 15 were injured.

In London, members of a Commonwealth delegation seeking to mediate between South Africa and the African National Congress, the main guerrilla group fighting white minority rule, said their initiative would continue despite the attacks.

South African military officials said Monday's raids in and around the capitals of Harare, Gaborone and Lusaka were aimed at ANC targets. It was South Africa's first major assault inside Zimbabwe and Zambia. Since 1980, the South African military has sent commandos against alleged ANC facilities in Lesotho, Mozambique and most recently Botswana, where 12 people were killed in a raid last June.

The attacks provoked an international outcry and were condemned by the United States, Britain, Australia, China, Tanzania and Kenya, among others.

Charles Freeman, a U.S. State Department official, said he had conveyed Washington's ''vigorous condemnation'' of the raids to Foreign Minister R.F. Botha.

''We stand with Botswana, Zambia and Zimbabwe in our sense of outrage that these attacks occurred,'' Freeman told reporters in Johannesburg before flying to Zambia to confer with the American ambassadors of the three raided countries.

In Johannesburg, about 800 students the University of the Witswatersrand skipped classes and gathered on a campus plaza, chanting and singing in protest against the raids. The university is integrated, with about 15 percent minority enrollment.

Lt. Pierre Louw, a police spokesman, said the rally was declared illegal. Authorities said 13 people, both blacks and whites, were arrested. Police said demonstrators threw stones at two police vehicles and several private cars. Witnesses said some of the protesters at one point rushed at a group of police, shouting ''Kill the Boers.''

Later today, about 2,000 people gathered at the university auditorium to hear speakers denounce the raid and demand the release of jailed ANC leader Nelson Mandela.

In another development, South Africa's currency, the rand, dropped sharply in value, and foreign bankers said the international outcry over the raids and fear of economic sanctions were the major causes.

The rand opened Monday morning, before word of the raids spread, at 45.8 U.S. cents. It dropped to 44.8 cents by the end of the day, and fell to 42.5 cents in early trading today.

In London, Gen. Olusegun Obasanjo, a member of the Commonwealth delegation, said ''the raids will have little effect on our peace effort.''

Obasanjo, a former Nigerian military leader, said the delegation, known as the Eminent Persons Group, met Monday with eight South African Cabinet ministers before returning to Britain.

''We had a frank exchange of views and the ball is now in their (South Africa's) court,'' Obasanjo told reporters at London's Heathrow Airport.

Another delegation member, former Australian prime minister Malcom Fraser, said in a television interview that ''it is still not impossible that there could be negotiations between the government and black leaders of all groups.''

The three attacked countries are members of the Commonwealth, a 49-member group of Britain and its former colonies. The delegation has been trying to lay the foundation for negotiations between South African and the ANC. One peace proposal would have South Africa release Mandela and recognize the ANC in exchange for a guerrilla cease-fire.

The group has said that unless firm progress is made, the Commonwealth was expected to impose economic sanctions against South Africa later this year.

Zambian President Kenneth Kaunda said the attacks could lead to some countries pulling out of the Commonwealth.

''There is definitely no point in continuing to belong to an organization whose ceremonial leader (Britain) has so openly sided with the enemy of most of the Commonwealth members,'' Kaunda said in Lusaka. He alleged that ''Britain has allowed herself to be used by America in propping up a racist regime to the extent that she now threatens the very existence of the Commonwealth.''

In Harare, the foreign ministers of the so-called frontline states - Angola, Botswana, Mozambique, Tanzania, Zambia and Zimbabwe - met for talks that had been arranged before the raids.

Zambian Foreign Minister Luke Mwananshiku said the raids were not the main purpose of the meeting, but said the ministers would ''also touch on the events that have just occurred.''

Editorial comments in South African newspapers today ranged from criticism to support.

The pro-government Citizen said the attacks were equivalent to the recent U.S. air strikes against Libya.

''We hope that countries like the United States and Britain will realize, after the heat of the moment, that South Africa has acted against the ANC in order to protect its own citizens from terrorist attacks,'' the Citizen said. ''In this, it is no different to the United States, which launched air attacks on Libya because of the terrorist activities masterminded by Col. Khadafy,'' the newspaper said.

Business Day, a Johannesburg financial newspaper, said the raids would have a severe effect on South Africa's economy, increasing pressure on foreign investors to withdraw.

''Behind the cry of 'terrorism' lurks a nastier word: Failure,'' said the editorial. ''The political failure is obvious to all; more worrisome is the implicit failure of the security forces within the borders, which forces them to seek politically sensitive targets farther afield.''