The ossified politics of South Africa were shaken and perhaps transformed this month by an accident of fate. It just may have been the first good political luck this country has ever had.

What happened could have happened only in South Africa: a conservative government proposed a phony reform, hoping to persuade foreigners (especially Americans) that it was moving toward a relaxation of the policy of apartheid that holds blacks so rigidly in an inferior status.

But before this Potemkin Village reform could make much of an impression abroad, it had an unexpectedly dramatic result at home. The government's proposals for constitutional changes to give new rights to colored (mixed blood) and Asian minorities -- but not blacks -- looked plausible enough to alarm a large portion of the government's own white supporters. As a result, the ruling National Party's Afrikaner power base has been slit wide open. Now, ironically, there is a genuine prospect of meaningful reform in the future.

This split became apparent earlier this month in a special election for a seat in the Transvaal provincial council that the National Party should have won with ease. In fact its candidate barely scraped by after losing half the white Afrikaner vote to a new conservative party formed only five months ago to resist Prime Minister P.W. Botha's reform proposals.

If indeed the Afrikaner vote is now deeply and irrevocably split, South Africa will never be the same. A real split could create an entirely new role for the integrationist Progressive Federal Party, the official opposition, which now holds just 27 seats in a parliament of 177. In the next election the progressives might pick up 50 seats, and in this new situation, that could be enough to hold the balance of power in the country between a minority National Party government and the rightists.

If they hold the balance of power, the progressives could persuade more moderate elements in the National Party to accept real reform in exchange for progressive votes needed to form a majority government. In this context, real reform would mean giving black Acricans some small but real role in the central government. This may be a slender prospect, but it at least offers the hope of new alignments and new movement where none existed before.

South Africa has been a de facto one party state for 34 years. If Prime Minister Botha's reform proposals bring an end to that condition, they will have more to commend them than was originally evident.

How this turnabout happened it worth examining.

Last month the South African embassy in London placed a full-page advertisement in the Financial Times under the heading, "The Changing Face of South Africa." with a number of photographs of blacks and whites fraternizing in various ways.

The sharp-eyed reader, looking closely at those pictures, would have noticed something odd. The largest photo was not of interracial fraternizing in South Africa at all, but of mining magnate Harry Oppenheimer and his lieutenant, Julian Ogilvie Thompson, with Mrs. Goatsive Chiepe, Botswana's minister of mineral resources, signing an agreement allowing the De Beers Corporation to open a new diamond mine in that country.

That photographic gaffe symbolizes the trouble with many claims being made about change in South Africa. They make a nice advertisement for foreign consumption, but closer examination often reveals somet after fiveshing fraudulent about them.

This was the case with Prime Minister Botha's new plan, announced last month, for extending political representation to the colored (mixed blood) and Asian minorities in separate parliamentary chambers.

It was presented as a great step forward and at first glance one is tempted to accept it as such. Despite the separation of the representatives and the continued total exclusion of the African majority, it is seductively encouraging to see the apartheid government at last proposing to put some non-whites in Parliament and possibly even th cabinet.

The accompanying argument was seductive too. It was that Botha has to advance cautiously to take his deeply conservative Afrikaner people with him. He must move first on the coloreds and Asians, then when his followers have become accustomed to that he can consider including the Africans. It has to be done in stages but at least he is moving in the right direction.

Unfortunately for those who advanced this argument -- Botha's allies -- it appears to have made a deeper impression on Afrikaners than on foreigners. Ironically, though, Botha's plan was not really leading South Africa towards integration, not even by stages.

His new constitutional plan is not to scrap but to modernize apartheid.

To appreciate this one must examine Botha's new constitutional plan in the context of actions his government is taking cncurrently against the African majority. They show what the real intention is.

The government's strategy is to draw the colored and Asian minorities into the system, hopefully making them allies of the whites but in a way that will not threaten Afrikaner control, while pushing the African majority further out to the periphery.

This is partly to create a new illusion of power sharing and a move away from racial discrimination, and partly a numbers game to reinforce the weakening numerical position of the whites in the over-all population.

Today the whites constitute 16 percent of a total population of 28 million. By the end of the century, they will be 11 percent of 50 million.

By coopting the 2.5 million coloreds and 850,000 Asians, the ruling oligarchy which Afrikaner nationalism still intends to dominate will be enlarged from 4.5 million to nearly 8 million.

Simultaneously, everything possible is being done to reduce the number of Africans who will be able to lay any future claim to political rights in South Africa. For them there is a policy of exclusion.

Pressure is being stepped up for the 10 little tribal homelands scattered about the fringes of South Africa to become independent. Four have already done so; another will soon. As this happens all members of the tribe concerned, whether they live in the homeland or not, are stripped of their South African citizenship and become statutory foreigners subject to deportation if they step out of line.

An authoritative study published recently by the Black Sash organization shows that 3 million Africans have been forcibly removed to rural slum camps in the tribal homelands over the past 20 years, and another 1 million are scheduled to be moved soon.

The populations of some of the smaller homelands have increased by between 200 and 500 percent over the past 10 years.

The number of Africans with the legal right to remain permanently in the cities is being reduced. Any rural African born after his homeland becomes independent cannot qualify for these rights.

Loopholes through which thousands of Africans used to slip into the cities illegally are being closed.

Many Africans used to be prepared to pay the penalty of a $100 fine or a spell in jail for the sake of a few months' work. This is being stoppped by a recent law which shifted responsibility on to the employer, who is not prepared to pay the penalty so does not offer the job.

The fine went up to $500 in 1979, and a new draft law proposes to increase it again to $5,000

At the same time, any African legally in a city, who accommodates another who is there in contravention of the strict influx control regulations, is himself liable to a $500 fine.

Thousands of Africans, many of whom have been in South Africa for decades, are being deported to neighboring Zimbabwe and Mozambique even when their employers want them to stay.

There is also an extraordinary attempt being made to give away two substantial regions of tribal land to the neighboring black state of Swaziland, against the wishes of the local inhabitants, so that another 1 million Africans can cease to be South African citizens and become Swazis.

While as many Africans as possible are thus being excluded, the coloreds and Asians are being co-opted. But while they are being made minority shareholders in white South Africa, Afrikaner nationalism will remain in control.

Botha's new constitution protects minority rule by putting overwhelming power in a new executive president.

The president will be chosen by an electoral college of 50 white, 25 colored and 13 Asian members of the proposed new tricameral parliament.

The whites will all be members of the majority party so its choice will be the man elected.

Each of the separate parliamentary chambers for whites, coloreds and Asians will legislate for matters of exclusive interest to its particular community, but all must pass matters of concern to the whole country.

But the president will retain massive discretionary authority. For example, he will decide which issues must be considered by which parliamentary chambers. And when there is a dispute among them, a new president's council, dominated by the executive, will make the final decision.

So the dominance of the National Party remains undiluted, even strengthened, given the unrestrained authority of the executive president. Not a shred of power is being given away or even really shared.

Why is there this renewed attempt, 20 years after Verwoerd's first reformulation of apartheid, once again to give the impression of change within a system which has as its bottom line the absolute necessity for maintaining Afrikaner control?

The short answer is that it is a periodic response to the buildup of pressures generated by an inherently unworkable system, which an embattled people must keep changing but dare not abolish.

At its center lies the imperative of Afrikaner survival as a heavily outnumbered white minority in a predominatly black country. Not just survival as a community, but as a national entity. Afrikaners, after a 300-year history in which they have evolved their own distinctive language from the Dutch of their forebears and their own cultural and religious heritage, have developed a strong sense of identity as a separate nation.

With this goes a deep conviction that if the Afrikaner nation is to survive it must have its own nation-state. No nation can exist as such if it is but a minority group in a country ruled by others.

This is why Afrikaner nationalist feel they have to remain in control of South Africa. It is why they equate integration with "national suicide."

It is also why, after an earlier anti-Semitism, Afrikaners understand so well the imperative need Jews feel for the state of Israel.

Yet how is a "nation" of barely 2.5 million to remain in control of a country of 28 million?

Straightforward domination was the initial method. But it soon became evident that this was no longer viable in the postwar world with its rejection of colonialism and its revulsion against institutionalised racialism.

The survival imperative operates in many ways. White South Africa may appear impervious to world condemnation, it is not. The desire for acceptance is almost at the level of a neurosis. In part this is plain human nature, but it is also because an embattled minority knows it is dangerous to be isolated without friends in a hostile world.

With this goes a diffuse awareness that a minority cannot dominate a majority in perpetuity, that ultimately survival will also depend on changing an unviable status quo.

There is a thin line between doing things to deceive others and doing them to deceive yourself when the only options open to you are unacceptable. If survival requires maintaining control in your own hands, but also requires that you end a system of domination which must eventually provoke a revolution, where is your choice to fall?

Probably on some complex formula that gives the impression of changing the old system while still retaining the essentials of it -- that tries to ward off the threat of revolution without letting go of total control.

This month's by-election results showed how risky it can be to try to live with the contradictions inherent in such a formula. By using the rhetoric of reform primarily to impress an external audience, Prime Minister Botha has sown mistrust among his own people. So now he is paying the political price for reformism without reaping any of its potential benefits.