A careful reading of what South Africa's leaders have done and propose to do with the country's policy of apartheid indicates that the bedrock fundamentals of the segregationist system are to remain firmly in place, despite shifts in their rhetoric.

With carefully shaded language, they have developed a code that can be read in different ways by different audiences. It wraps old practices in new euphemisms, putting a gloss on marginal reforms for the benefit of foreign critics while reassuring the folks at home that the essentials of the old system will remain.

This ambiguity was clearly demonstrated last week when a key member of President Pieter W. Botha's Cabinet told Afrikaner members of the Railway Women's Association at a gathering in the industrial city of Kempton Park, east of Johannesburg: "Our youth must prepare themselves for drastic political changes in which the white position of dominance will be exchanged for one of partnership with the blacks."

Within hours, that speech by black affairs Minister Gerrit Viljoen was the lead item on BBC World Service newscasts, adding to the surge of international anticipation that Botha was about to make a momentous pronouncement ending South Africa's apartheid system of white-minority rule.

What the BBC and its overoptimistic listeners in western capitals overlooked is that the conservative white women railroad workers showed little sign of consternation as they left the meeting. Viljoen had assured them that the "drastic changes" would not alter the things they cared most about. Segregated schools, segregated living areas, segregated politics would all stay, and the "inherent ability and will of the white nation to maintain its identity" would continue to be decisive in South Africa's affairs.

While the BBC was raising hopes abroad about the demise of apartheid with its coverage of the speech, the Financial Mail, South Africa's leading business magazine, was reporting that Viljoen had announced the entrenchment of apartheid's fundamentals.

In the postmortems following widespread disappointment, particularly in the United States, at Botha's failure to announce expected reforms last Thursday night, it is being suggested here that a misunderstanding of South Africa's code language may have accounted in part for what Pretoria is now claiming were unjustified expectations.

Chester Crocker, U.S. assistant secretary of state for African affairs, has frequently alluded to this code, saying the Botha government uses it to avoid alarming its conservative, white supporters, and that outsiders have to understand it in order to grasp the significance of Botha's reformist intentions.

But some observers are beginning to ask whether Crocker and other U.S. diplomats, in their eagerness to read optimism into the South African situation, are not misinterpreting the code language and concluding that Botha means to do more than he actually says he is going to do. Gap in Perceptions

Frederik van Zyl Slabbert, leader of the opposition Progressive Federal Party, believes that this widening gap in perceptions reached a critical point of public exposure with Botha's speech last Thursday.

"The thing that people have consistently overlooked is that P.W. Botha has never lied about what he intends doing," Slabbert said in an interview.

" Foreign Minister Roelof Pik Botha may have sold a line, but never P.W. He has always been straightforwardly honest in saying that he is not scrapping any of his party's basic principles. The trouble is people just don't believe him. They keep reading into what he says intentions that are not there. They don't take the man at face value."

President Botha and his constitutional affairs minister, Chris Heunis, have spelled out in some detail what their constitutional plans are. Botha said on Thursday that he regarded the speech he was making then, together with another delivered in January, as his "manifesto."

Many of the ideas set out in the manifesto already have been implemented. A think tank of young political scientists attached to Heunis' Department of Constitutional Development in Pretoria is constructing models for those sectors of the evolving structure that have not yet been completed, working according to guidelines laid down in Botha's speeches.

What is emerging would seem to leave little room for the persistent attempts, both in South Africa and in some western capitals, to portray Botha as a leader who wants to dismantle the system of white-minority domination and replace it with multiracial government, and whose hesitation and backsliding are attributable to the need to take his conservative, white electorate with him.

As Slabbert points out, the system that is being constructed is based on the old apartheid structures: legally defined and classified race groups, living in separate areas and exercising their political rights through separate institutions. White political control at the top remains entrenched and is regarded by Botha as nonnegotiable.

What is different is that blacks are being offered a greater say in administering their own affairs in the areas where they live, and provision is being made for some degree of consultation with them at higher levels of government.

"In terms of Afrikaner nationalist ideology, those changes are quite dramatic," Slabbert said. "But they are all within the same political framework. The basic structures remain. It still means that the real power is in white hands and that the upwardly mobile young black cannot jump out of his ghetto. That is why it can make no impact on the black community or do anything to defuse the unrest."

Herman Giliomee, a respected Afrikaner academic, sees the thrust of the government's reforms as "an attempt by the Afrikaners to find the secret of sharing power without losing control."

The government is making a show of consulting with blacks, Giliomee says, but it is not prepared to move outside the apartheid framework with any of the changes it makes. This makes the reforms unacceptable even to moderate blacks such as Zulu leader Chief Gatsha Buthelezi and paints those with whom the government does talk as "collaborators" in the eyes of radicals. A Taste for Euphemisms

The language of apartheid also is changing. The South African government has always had a taste for euphemisms in its attempts, as a critic once put it, to "Max Factorize" the face of apartheid. Thus the name of the massive government department that governs the lives of the 21 million blacks in the manner of an internal colonial administration has changed over the years from the Department of Native Affairs, to the Department of Bantu Administration and Development, to the Department of Plural Relations, to, currently, the Department of Cooperation and Development.

Apartheid, known originally as wit baasskap, the Afrikaans phrase for "white mastery," was later changed to "separate development," and Botha has lately taken to calling it "cooperative coexistence." Three days ago, government statements suddenly began referring to black townships as "black residential areas."

The code of euphemisms becomes more misleading when it is applied to the reformist ideology. The Botha manifesto states that blacks are to be given political rights that will enable them "to decide on their own affairs up to the highest level."

That does not mean they are to be given representation in the national legislature. Botha's policy rules out such a possibility, even in the form of another separate parliamentary chamber similar to those already given to the mixed-race and Asian minorities.

The key to the code in this case lies in the phrase "own affairs." Blacks are to be given some form of an as yet unspecified national body that will have legislative authority over matters of exclusive concern to the 10 million blacks who live outside the designated tribal "homelands." It will have no say in matters affecting the white, mixed-race and Asian groups, and it will not form part of Parliament, although some political scientists believe one or two members of such a body might be appointed to the president's Cabinet.

That is the most that the Botha manifesto envisions for the black majority in the way of political rights.

In his speeches, Botha states that the political system being evolved is "unique" and designed to cater to what he regards as South Africa's "unique situation." In another of the code phrases, this unique situation is described as one in which South Africa does not have a white minority and a black majority, despite its 4-1 population ratio.

"It is," says Botha, "a country of minorities -- white minorities and black minorities."

This demographic miracle is achieved by dividing the blacks into separate tribal "nations," none of which then constitutes a majority of the total population. To maintain semantic consistency, government spokesmen never refer to "the people of South Africa"; they always use the plural, "peoples," to denote the country's "multinational" character.

Extrapolated from this is the whole concept of "cooperative coexistence," which is the theme of the Botha manifesto. Each "nation" must have jurisdiction over its "own affairs." Institutions then must be established for links with the central government on what are called "general affairs."

Municipal councils have been established for many black, colored (mixed race) and Asian townships. In January, regional services councils will be appointed, with representatives from these nonwhite township councils and from white town and city councils, to administer water, electricity, sewerage and other services on a regional basis.

Representation in these regional councils will be based on taxes paid by the inhabitants of each of the segregated towns, which means the affluent whites will dominate them.

Provincial councils, similar to but less powerful than state legislatures in the United States, will be abolished between April and June next year. Each of the four provinces will be administered by an administrator, who is a kind of governor, and an executive committee to be appointed by the president. Nonwhites may be included on these appointed executive committees, and multiracial advisory committees, "linked to the various ethnic electorates" in a manner not yet specified, will consult with them.

At the national level, coloreds and Asians already have been given subordinate parliamentary chambers, with authority over their "own affairs" under a new constitution introduced last year. Legislation affecting "general affairs" has to be passed by each of the three segregated chambers of the new Parliament, but if one chamber vetoes a bill, a President's Council dominated by white appointees has the power to pass it into law.

Blacks were excluded from the new constitution, and it is Botha's plans for them that have been the main subject of speculation over the past year.

In his January manifesto speech, Botha accepted for the first time that the 10 million blacks outside the 10 tribal "homelands" earmarked for nominal independence were permanently part of South Africa, entitled to more political rights than those offered by their township councils.

"Structures" would have to be developed for them, Botha said, so that "they can themselves decide on their own affairs up to the highest level." But he repeated that these "structures" could not take the form of a fourth chamber of Parliament. No Specific Blueprints ----

The political scientists in Heunis' Pretoria think tank, who say they are not drawing specific blueprints but preparing options that can form the basis of negotiations with black leaders, admit that Botha's restriction allows for few options.

An obvious one, they note, is a national council for blacks that would not be part of Parliament but that could be given legislative authority for blacks' "own affairs."

Or there could be an "informal cooperative body" in which blacks could be consulted on "general affairs" and be given authority over their "own affairs." There are hints that the government is thinking of turning the President's Council into such a body, appointing representatives from the black Urban Councils Association to it, at the same time removing the President's Council's powers of adjudication in parliamentary deadlocks and handing these to a new white-dominated "constitutional court."

The Botha manifesto also states that whatever "structure" is decided on for urban blacks should also serve to link them, the homeland administrations and the central government on "general affairs." The think tank staff members hint that this means Botha could appoint some blacks from there to his Presidential Cabinet, as he has already done with the coloreds and Asians.

The key to the entire structure is that central government remains firmly under white control, with a constitutionally entrenched white majority in Parliament that ensures that the powerful executive president will always be the leader of the majority white party. Emphasis on Stability

Continued white, and specifically Afrikaner, control is considered essential to the maintenance of stability, Giliomee says. He believes it has become a secondary theme of the new reformist ideology that Afrikaner nationalism provides the "stable center" of South Africa.

"An Afrikaner leadership is considered the only one which can both enjoy the trust of the core ethnic group and successfully direct all the technocratic skills and abilities which serve the material welfare of everyone in the country," Giliomee contended. "If this stable center loses its coherence everyone will suffer as a result of the inevitable loss of stability and efficiency."

Botha seemed to underline this theme in his Thursday speech when he said: "Destroy white South Africa and our influence, and this country will drift into faction strife, chaos and poverty."

Heunis has been even more specific. "It is in the long-term interests of South Africa that the Afrikaner should always have the leadership role," he said in a speech a few years ago, adding paternalistically that "this role of leader will be accompanied by ever greater responsibilities."

The object of Botha's policy changes, therefore, appears to be an Afrikaner-led white "nation" in which the various nonwhite ethnic "nations" are accommodated, given the right to run their own community affairs as far as this is practical, and consulted by the government in matters of concern to the country as a whole.

As Slabbert says, in terms of Afrikaner nationalist ideology the changes are considerable. From that viewpoint, Botha has made a daring and generous gesture. From the black nationalist viewpoint, it is a cynical attempt to gild an evil system.

Under the pre-Botha apartheid system, all the country's 21 million blacks, regardless of where they lived, were assigned according to their ethnic origins to the tribal homelands, which were supposed eventually to become independent nations.

As each homeland was given nominal independence, all members of the tribe officially assigned to it became citizens of the new country and ceased to be South African citizens. The idea was that they would then cease to have any further moral claim to political rights in the 87 percent of South Africa regarded as the white nation's homeland. Eventually, as all the homelands became independent, there would be no more black South Africans.

Although nearly half the total black population lives outside the homelands, and many have been in the big industrial cities for generations, they were still regarded as "temporary sojourners" there and could not buy property or acquire permanence.

Botha is changing much of this. In his speech in January he accepted the permanence of the black city dwellers and announced that they would be given the right to buy property. He also said that he would reconsider their citizenship status and modify the influx control regulations that restrict the movement of blacks into the cities.

Most informed observers expected him to announce these two reforms, but not much more, in his Thursday speech, but Botha merely repeated his intention to review both issues.

An announcement is thought likely soon in which a distinction will be drawn between "citizenship" and "nationality," enabling blacks, in characteristically ambiguous fashion, to be made citizens of South Africa and nationals of their homelands.

Botha has said he will modify, though not abolish, the influx control regulations. Slabbert, who is the opposition party's constitutional specialist and monitors the government's reformist thinking closely, points out that if a national council for urban blacks is to be established, then the influx laws remain essential to provide a legal definition of urban blacks as distinct from homelanders.

Despite the limited nature of the reforms and the fact that blacks dismiss them as irrelevant, observers such as Slabbert and Giliomee believe that they may yet turn out to have an unforeseen importance, if only by breaking up an ideological logjam that has existed for several generations.

Slabbert, who is a former sociology professor, talks of a possible "chain reaction of unintended consequences" as Botha and his political scientists reorder a rigid system. But he stresses the lack of intent on Botha's part: "Anyone who believes P.W. is trying to bring about a major political reform is a victim of his own wishful thinking."