LONDON, JULY 7 -- Despite strong disapproval by the government of President Pieter W. Botha, 67 whites, most of them prominent Afrikaners, left South Africa amid heavy publicity last night for an unprecedented four-day conference with leaders of the outlawed African National Congress in the Senegalese capital of Dakar.

The group assembled in London today for an initial briefing on the secretly organized conference, which will be followed by a 10-day tour of West African countries that for most will be their first venture into black Africa.

They will fly to Dakar via Paris Wednesday and begin the conference Thursday with a 16-member ANC delegation led by information chief Thabo Mbeki.

The mission, led by former opposition leader Frederik van Zyl Slabbert, has aroused intense interest in South Africa since word of it leaked last Thursday.

The government -- involved in a campaign to discredit and neutralize the black nationalist organization while attempting to draw what it regards as moderate blacks into negotiations about the country's future -- is angry about the meeting, which it sees as cutting across its strategy and boosting the ANC's image.

Critical comments in progovernment newspapers yesterday led to fears that the authorities might intervene to stop the group from leaving the country. But in the end they left unhindered.

The identity of those in the group was kept secret until they had boarded their aircraft at Johannesburg airport as a precaution against them having their passports withdrawn.

They include a number of academics, writers and business and professional people, all of them verligte, or liberal critics of the Botha government, but many with close ties to the Afrikaner establishment.

Among them is Abraham Viljoen, brother of the recently retired chief of the South African Defense Force, Gen. Constand Viljoen.

Abraham Viljoen is a retired professor of theology at the University of South Africa in Pretoria. Theuns Eloff, chaplain at Pretoria University, the biggest and most conservative of the Afrikaans universities, also is in the group.

Others include Pieter Schoeman, nephew of a former leader of the ruling National Party, and Riaan deVilliers, a journalist and the son of the retired head of a major pro-government newspaper company.

Other well-known names are Beyers Naude, a dissident Afrikaner theologian who retired last week as head of the South African Council of Churches, and Andre P. Brink, a leading Afrikaans author.

Most members of the group hold key positions in Afrikaans universities and other institutions, but have disagreed in private with government policies. Some are emerging publicly for the first time.

The bitter tone of some of the newspaper comments reflected the level of the government's anger at the mission.

Referring mockingly to "this latest safari" and to Slabbert as "a discredited politician who deserted his own party," Die Burger, which speaks for the ruling National Party in Cape Province, said the mission was an exercise in futility that could only boost the ANC's image.

"Without a mandate from anyone this has-been, with a following of parvenus from the political fringe, is now going to confer with the instigators of a terrorist war," the paper said.

The Citizen, of Johannesburg, also accused the group of boosting the ANC's image and hinted that the government might retaliate against Slabbert's newly established organization, the Institute for a Democratic Alternative for South Africa, by using a special security law to cut off its foreign funding.