In an effort to win credibility among Namibia's black majority, the South African government has given the administration it installed here on Monday greater powers than its predecessor and included in it members with authentic African nationalist backgrounds.

The new administration needs credibility to counter the popular liberationist image that SWAPO, the South-West African People's Organization, has built up during a 17-year guerrilla war for independence.

To this end, Pretoria has given it more power than a previous internal government headed by Dirk Mudge, which South African Prime Minister Piet W. Botha dissolved two years ago because he considered it a failure. South Africa has occupied and controlled Namibia since World War I, ignoring since 1966 United Nations efforts to assure the country's independence.

South Africa is handing over to the new administration all powers of self-government except foreign affairs, defense and internal security. The administrator general, a South African official who has run the country as a kind of viceroy, will retain a power of veto, but this is expected to be used with restraint.

Unlike Mudge's administration, which was seen as Pretoria's puppet, the new one includes some members with authentic African nationalist backgrounds, notably Moses Katjiuongua, 43, leader of the South-West African National Union (SWANU).

SWANU has been in the independence struggle since before SWAPO was formed, but is less powerful because it is rooted in the Herero tribe, which makes up only 6 percent of Namibia's population, while SWAPO's base is the Ovambo tribe, which makes up 53 percent.

Katjiuongua served a long radical apprenticeship in exile, much of it in Peking. He appeared at the June 17 inauguration in a Mao Tse-tung suit, lending an incongruous touch to a ceremony presided over by conservative white Afrikaners, who support strict policies of racial segregation.

Andreas Shipanga, one of the founders of SWAPO who later fell out with its leader, Sam Nujoma, and formed his own breakaway party called the SWAPO-Democrats, is another leader in the new administration.

Both Katjiuongua and Shipanga say they will be able to introduce important reforms and dismantle the segregationist system of apartheid that South Africa has extended to this former German colony during its 67 years of control.

"The whole [United Nations Resolution] 435 initiative is stalled, and there is no prospect of it moving again in the near future," Katjioungua said in an interview. "We must try to find another road to independence, and I believe we can achieve enough to jolt SWAPO into negotiating a settlement that South Africa can accept."

SWAPO members in Windhoek scoff at the prospects of the strategy to force them into the government. They say there is no chance of the organization as a whole, or any of its senior members, agreeing to participate in what its vice president, Hendrik Witbooi, denounced at a meeting Monday as a "conspiracy" and "a step backward in the history of our country."

It will not be easy for the new administration to gain the credibility it needs. It is unelected and unrepresentative of the population. South Africa is simply handing power to a loose alliance of six anti-SWAPO parties who are prepared to cooperate with it, the biggest still being Mudge's Democratic Turnhalle Alliance, which has been given three Cabinet seats while the other parties get one each.

The same ratio has been used to establish a wholly nominated National Assembly of 62 members. The result is lopsided, giving the 7 percent white population two Cabinet ministers, the 6 percent Hereros two and the 53 percent Ovambos one.

Western observers have said that the new administration is just another effort by South Africa to sidestep a U.N.-approved independence plan and keep some control over the territory's affairs.

Shipanga says he has no illusions about South Africa's intentions, but denies that he is allowing himself to be used. Pretoria would go its own way regardless of him, he said.

"Our country is rotting internally," he said. "It is being run by South African colonial officers who have little real concern for our people and they are letting it rot. At least now we will be able to run the place ourselves and get a few things done."