SALISBURY, Zimbabwe-Rhodesia - The new black majority government of Zimbabwe-Rhodesia celebrated its first holiday in late July, honoring the founder of white Rhodesia, Cecil Rhodes, the epitome of 19th century British colonialism.

Laughing over the irony, Atherton Mpisaunga said the holiday illustrated the major fault Africans are finding with Prime Minister Abel Muzorewa's two-month-old government.

"The government is so busy trying to reassure the 250,000 whites that it has forgotten all about the 7 million blacks in the country," he said. Just last April, Mpisaunga went to the polls to vote for Murzorewa, full of hope that the new government would bring peace and prosperity.

Many Africans are voicing similar criticism of the lack of change, although there still is sentiment that perhaps two months is too short a period to judge Prime Minister Muzorewa's black-led government.

Officials freely admit that the main concern of the new government has been to reassure whites that there still is a place for them in this attempt to build a multi-racial society after 90 years of white domination.

"This is an evolutionary, not revolutionary, government," said Deputy Information Minister Ishmail Adam. "Revolutionary changes would result in absolute chaos."

Thus a visitor sees only white faces at the Department of Information. Even all the secretaries are white. One official points out that one black has been brought into the department but nobody makes an effort to produce him.

The need for efficiency is often cited as the reason for the lack of change.

"They've replaced three white stenographers with seven blacks" at Muzorwe's office, "which tells you something about their efficiency," one white said."Just try to phone the prime minister's office and you'll see."

Adam admits that no programs have been instituted yet to accelerate training of blacks to take over higher level positions. He cited the country's concentration on fighting a guerrilla war that is costing it more than $1 million a day, almost 40 percent of the budget.

For the embattled Muzorewa, plagued by unending war and slipping black support, the problem is whether such slow evolutionary change will be good enough to keep him in power.

He appears to be in a classic no-win position. He must assuare the fears of the whites to stem their continuing emigration at the rate of 1,000 to 1,500 a month, since they form the backbone of the economy and the military defending the government.

Yet at the same time he must produce enough gains for blacks to maintain their support and win recognition from the outside world that Africans are truly in control. Not even the most optimistic official claims he has done so. The constant litany is, "Give us time."

Some white officials do not make Muzorewa's job any easier in trying to reflect the image of a black prime minister in control. One said bluntly, "We had to remind Murzorewa four weeks after he had taken office that he had not yet addressed the country and perhaps it would be a good idea if he did so."

It is said that one of the prime minister's first activities every morning is to visit the office of Gen. Peter Walls, armed forces supreme commander, to get a briefing on the war. Both blacks and whites point out that under the white government of former prime minister Ian Smith there was a not-so-subtle difference - Walls went to Smith's office.

There is a feeling that Walls has replaced Smith as the man behind the scenes pulling the strings, meaning in effect that a white military coup has taken place within the new black-led government. This would make Smith all the more expendable as an eventual bargaining chip with the West.

On the other hand, the new Zimbabwe-Rhodesia government phonebook lists Smith's office as being in the headquarters of combined military operations, hardly a place for him to wither away in obscurity.

There have been some changes favorable to blacks, however.

Although whites still retain the majority on the important three-man Civil Service Commission that controls appointments, A black has been sworn in. An African is expected to be appointed soon to the high court, where strict qualifications have frozen out blacks. An African has become the second highest ranking official in the western city of Bulawayo.

The gradual desegregation of some Salisbury neighborhoods has been continuing quietly for more than a year. One suburb that was all-white a year ago is about 40 percent black now, indicating some degree of white flight.

But U.S.-educated Stanlake Samkange, an opposition member of Parliament, said, "The whites have behaved magnificently in this [housing] situation. There have been no racial clashes like in the United States when neighborhoods integrated."

Muzorewa's main problem is that the six-year-old guerrilla war is continuing without letup, killing an average of more than one person every hour.

He has pinned his hopes onl lifting of economic sanctions and recognition from the West, plus an amnesty program to lure away many of the 13,000 guerrillas in the country.

On the first issue, his fate rests with British Prime Minister Margaret Thatcher who appears to be ready to life sanctions if she can mute black African reaction.

Salisbury officials say there is no question that Britain, followed by the United States, will life sanctions. The only question, they say, is when and how it will come about.

Repeated amnesty efforts have been unsuccessful. The latest effort two weeks ago got off to an inauspicious start, coming just a day after government security forces killed 183 black paramilitary troops organized in party "auxiliaries" designed to support the government.

Although the military said the mass killing occurred during effotts to rein in the "ill-disciplined auxiliaries," the message must have been clear ot the guerrillas: If this is what you do to your friends, how will you treat your enemies?

In the African suburbs of Salisbury, the incident was seen as an outright massacre.

The lack of black confidence in Muzorewa also is reflected in complaints that two months after Africans took power they are still being aksed to salute the white Rohdesian flag and sing the old national anthem.

These changes take time, said Deputy Minister Adam. CAPTION: Picture, ABEL MUZOREWA