The ''crisis'' of southern Africa does not threaten to embroil the world as does, for instance, the one in the Middle East. But whatever southern Africa lacks in strategic importance, it makes up for in moral relevance, close observers say. Nowhere do the odds seem longer or the need greater for blacks and whites to find a formula for peaceful coexistence.
Many experts say the United States is in a unique position to help ameliorate and defuse the situation in southern Africa. And many of those living in the region are looking to the United States with a new sense of urgency.
That sense springs from white-ruled South Africa's use of its military and economic weight to neutralize basically hostile neighboring black governments.
In the short term this South African policy appears to be working. But many analysts worry that, as long as Pretoria's internal policies generate resistance from its own black majority, a few emerging signs of regional calm may simply mask potentially greater turmoil.
Blacks in southern Africa generally see the racial policies of Pretoria's white minority government as the fundamental cause of turmoil in South Africa and the region.
South Africa is the only country in the world where racial segregation is fully institutionalized and endorsed by law in all spheres. Under apartheid, all economic and political control is in the hands of some 4.5 million whites.
There are moves to bring two other relatively small population groups - the 2 .6 million Coloreds (persons of mixed race descent) and 800,000 Indians - into Parliament as junior partners with whites, but 22 million blacks remain excluded from any role in central decisionmaking.
The United States has a central role to play in southern Africa because it is in a position to talk both to Pretoria's white rulers and to blacks who oppose the regime, many analysts say.
The US has a measure of credibility with blacks because of its own steps toward racial equality and justice, its experience in grappling with civil rights issues, and its lack of taint as a past African colonial power.
But strong economic, resource, and strategic interests in southern Africa have made it essential that the US maintain a dialogue with Pretoria. Also, in terms of East-West rivalry, the US values white-ruled South Africa as a buttress against Soviet ''meddling'' in southern Africa.
These somewhat conflicting interests may give the US an opportunity to be a mediator in southern Africa, but they also pose a challenge for US policymakers.
For more than 20 years, Democratic and Republican administrations have tried to find the right combination of ''carrots'' and ''sticks'' to move South Africa toward peaceful, evolutionary change. So far, many of their fundamental objectives have not been realized.
What does the US want to achieve in southern Africa?
Helen Kitchen, director of the African Studies program at Georgetown University's Center for Strategic and International Studies, says the ''tactics and rhetoric'' have changed under different US administrations. But the basic policy goals remain fairly constant.
First and foremost among those goals, Kitchen says, is a settlement that would bring independence to Namibia (South-West Africa), Africa's last colony. South Africa continues to administer the territory in defiance of the United Nations and of a ruling by the International Court of Justice.
Despite years of negotiations with the so-called contact group (the US, France, Britain, West Germany, and Canada), Pretoria has for one reason or another refused to implement the United Nations plan for Namibian independence.
Kitchen cites two more goals of US policy: (1) internal reform in South Africa that could lead to a government that would rule with the consent of the governed, and (2) regional peace and stability that would allow for greater economic prosperity for all of southern Africa.
But even if US goals have been consistent, the ''tactics and rhetoric'' have varied, with important consequences, close observers say.
The Reagan administration has practiced a policy it calls ''constructive engagement'' toward South Africa and the region. The most noticeable and controversial feature of the policy is its milder rhetorical tone and infrequent criticism of Pretoria's racial policies.
The architect of the policy is the US assistant secretary of state for African affairs, Dr. Chester Crocker, who has called for a ''tone of empathy'' not only toward blacks who suffer in South Africa's ''racist system'' but also for the ''awesome political dilemma'' facing the ruling whites.
The Reagan team has operated on the assumption that it will have more leverage with Pretoria if it desists from the type of harsh criticism the US often issued in the Carter years.
The quieter Reagan approach has created a view among many South African blacks that the US supports the status quo in South Africa. Reagan administration officials deny this, but they concede their approach may not be popular. Nevertheless, they insist they will help blacks more in the long run by getting concessions from Pretoria than by simply ''saying the right things.''
The Reagan emphasis on encouraging white-led change signals to many blacks in South Africa that the US is supporting the so-called ''reform'' initiatives of South African Prime Minister Pieter W. Botha. The US has given the strong impression that it supports Botha's proposed new constitution, which would bring Coloreds and Indians into Parliament.
South Africa's blacks see the new constitution as a final step to exclude them from political rights. Black Zulu Chief Gatsha Buthelezi has called the Colored Labor Party's decision to participate in the new parliament ''a slap in the face'' for blacks.
But strong rhetoric can be counterproductive, some analysts say. Harsh criticism and absolute demands have at times made Pretoria dig in its heels.
One example is the 1977 meeting between then US Vice-President Walter Mondale and the late South African prime minister, John Vorster. Mondale reportedly implied the US wanted a one-man, one-vote system in a unitary South Africa. Vorster won a landslide election victory later that year on a platform of resisting outside meddling. Most analysts say a careful blend of ''carrots and sticks'' is the best formula for influencing South Africa. They say a major problem with US policy is that the blend varies. The Carter administration, for instance, softened its rhetoric toward the end of its term. Some analysts say the Reagan administration is subtly stepping up its criticism of Pretoria.
How influential is the US with South Africa?
The US was its top trading partner in 1982. US direct investment in South Africa exceeds $2.6 billion, and more than 300 American firms do business here.
Still, the US ambassador to South Africa, Herman Nickel, says, ''Our influence is not nearly as great as people both here and in the United States assume.'' He describes the US role this way: ''What we can do is to add our voice and influence to forces that are already at work here. If we carefully husband our influence for cases in which it can make a difference, there is a chance it can tip the scales.''
Both Ronald Reagan and Jimmy Carter wanted a Namibia settlement, and both have found it elusive.
The Reagan administration made Namibian independence a top goal, and through at least its first two years in office regularly signaled that a settlement was near. As a number of analysts see it, Washington expected its softer criticism of Pretoria to pay off in Namibia. But the ''payoff has not yet come'' and black disenchantment with ''constructive engagement'' is deepening, analysts say.
Even so, the Reagan administration claims progress on Namibia. Washington says it inherited a moribund issue and has given it new momentum. Indeed, Pretoria has said all the major issues regarding the carrying out of the United Nations Security Council plan for Namibian independence have been settled.
The remaining obstacle is the estimated 25,000 Cuban troops in Angola. Angola and other black governments say the Cuban issue is a pretext for further South African delays. South Africa - with US backing - says free and fair elections in Namibia are impossible with Cubans stationed in neighboring Angola.
The most recent Reagan administration achievement is its involvement last week in working out a formal cease-fire between South Africa and Angola. The US itself has agreed to help monitor the peace in southern Angola if both sides ask it to so. Some analysts say this development signals that the Reagan administration is more confident that prospects for a Namibia settlement have improved.
But the as-yet-unresolved issue of Namibia may indirectly have had a positive impact on the US role in southern Africa, some analysts say.
John Dugard, a professor of law at the University of the Witwatersrand in Johannesburg, says that when the Reagan administration became convinced in late 1982 or early 1983 that Namibia issue was not going to be resolved quickly, it apparently shifted gears and applied more pressure on Pretoria on certain internal issues.
''In 1983 the US engaged in visible, voluble diplomacy,'' Mr. Dugard says. He sees some results, too.
Last year South Africa's highest court opened the way for more blacks to live and move more freely in urban areas. Pretoria immediately signaled it would overrule the court with new legislation that would preserve South Africa's maze of restrictions on where blacks can work and live.
The US then strongly and publicly praised the court decision. And although Pretoria has acted to weaken the decision, it has not altogether overturned it.
''This was a case in which a strong public statement (by the US) had a positive effect,'' says Dugard.
The ultimate ''stick'' is economic sanctions and disinvestment. Some black activists say the imposition of sanctions is the only acceptable policy for the US. Some US critics of South Africa advocate this not because it might create change in South Africa, but because they think the US has a moral obligation not to deal with Pretoria.
Other analysts question the effectiveness of sanctions because they do not always have the intended effect. For instance, the UN adopted a mandatory arms embargo against South Africa in 1977. South Africa countered by building its own arms industry. It is now the 10th largest in the world and aggressively seeks export markets.
Another example: After Arab countries embargoed oil sales to South Africa, this country became a world leader in the production of synthetic fuels from coal.
No one is sure what effect further sanctions would have.
Opponents of disinvestment believe US firms can be pace-setters for fair labor practices here. Some 146 US firms doing business here have signed the so-called Sullivan code of labor practices, which supports complete integration in the workplace; equal pay and employment practices; and programs to advance the training of black employees and to improve their living conditions.
''There is little doubt that the labor practices of many American companies in South Africa have changed significantly for the better in the past few years, '' says John Kane-Berman, director of the South African Institute of Race Relations.
Within South Africa prominent black activists like Winnie Mandela, wife of imprisoned African National Congress leader Nelson Mandela, see no advantage to US investment in South Africa. ''We don't want people to promote apartheid by investing in this country, and doing so at the expense of the black man,'' she says.
Regionally, the credibility of ''constructive engagement'' has been tarnished by South Africa's strong-arm tactics. Since 1981 South Africa has launched three cross-border strikes into Mozambique and one into Lesotho - allegedly against the outlawed African National Congress, which has tried to build black resistance to Pretoria.
On other occasions Pretoria has invaded Angola to strike against SWAPO (South-West Africa People's Organization) fighters seeking to end South Africa's rule over Namibia.
Such actions against its neighbors seem to belie one premise of ''constructive engagement'' - that South Africa has an interest in regional stability and that stability would encourage Pretoria to move more rapidly on internal reforms.
South Africa has also intimidated all the states with which it has common borders from materially supporting the ANC. Mozambique recently met with South Africa and agreed, at least in principle, that neither side should be used for acts of aggression against the other.
Diplomatic sources say the US was a ''key catalyst'' in the South Africa-Mozambique talks. They also claim the US was a ''significant factor'' in bringing South Africa and Lesotho to an agreement on curbing the ANC after Pretoria raided alleged ANC homes in that country and squeezed Lesotho economically.
But just what did the US achieve in Lesotho and Mozambique? It appears the US was not able to stop Pretoria from hammering these countries militarily. The US efforts appear to have been ones of damage control, helping to end situations of potentially escalating conflict.