Johannesburg — The atmosphere is euphoric. The chant starts in one corner and soon reverberates through the entire assembly hall:
''Tambo is in the bush and training the boys, Tambo is in the bush and training the boys.''
This is a political gathering of blacks in South Africa. Undaunted by the white security police openly filming the meeting or the truckload of soldiers parked three blocks away, the blacks are showing their support, almost reverence , for the outlawed African National Congress (ANC) and its leader, Oliver Tambo.
The ANC, dedicated to ending white control in South Africa, has always been met with hostility by the government here. But harder times may be just ahead for Tambo and his boys, as well as for the black masses in South Africa that draw hope and inspiration from the challenge the ANC has posed to Pretoria since 1977.
Experts on the ANC say it soon may be forced to reconsider its strategy in South Africa. Seven years of rising sabotage by the ANC have earned it broad black sympathy in South Africa and an international reputation as the liberation movement in the country.
But the ANC's guerrilla activity may now be considerably more difficult to carry out because South Africa is exerting strong and effective political and economic pressure on the black states that have lent support to the black nationalist group. The result may cause a backlash that could make violence increasingly unattractive to the organization, analysts say.
This could have an important effect on internal black politics in South Africa, say experts on black politics here.
Various internal movements could be affected in specific ways. It could boost the political standing of the adherents of black consciousness who have long opposed the ANC because it permits white involvement. Blacks who for either strategic or moral reasons have rejected violence may also gain some new political support.
But the most profound impact, some analysts say, could be a reinforcement of the message to blacks that their struggle against white-minority rule in South Africa will be a long, hard one that for the foreseeable future will not be won at the point of a gun.
Pretoria has never regarded the ANC as a true military threat. And experts say the ANC uses violence mainly as a propaganda tool, recognizing it is not capable of doing serious military damage to South Africa.
But Pretoria's regional military might, amply demonstrated over the past three years or so, threatens to knock out even the nagging effect of the ANC's insurgency campaign.
South Africa has come very close to neutralizing the ANC militarily by forcing compliance from the neighboring black states that provide the ANC access to South Africa. Swaziland, and to some extent Lesotho, have helped Pretoria evict ''refugees'' that South Africa claimed were ANC activists.
Botswana and Zimbabwe studiously seek to keep any ANC military activity away from their territories.
Most important, Mozambique has agreed to a formal security agreement with South Africa that includes new controls on the ANC.
South African officials claim that more than 90 percent of the sabotage in South Africa in recent years ''originated'' in Mozambique. These officials concede there are no major ANC training bases in Mozambique, but allege that most attacks are planned and staged from Mozambican soil.
What Mozambique apparently gets in return for its rapprochement with South Africa is Pretoria's lessening of support for that country's Mozambique Resistance Movement and a ''normalization'' of the economic relationship between the two countries. Mozambique is highly dependent on South Africa economically and has been severely hurt not only by Pretoria's military actions but also by the economic dislocations they have caused. Further, Mozambique is in the midst of a devastating drought that has caused large-scale starvation.
South African security officials are brimming with confidence that 1984 will be a turning point against the ANC. These officials say they hope to ''substantially reduce'' sabotage within South Africa this year, with compliance from neighboring black states.
However, these security officials say they do not expect ANC activity to disappear completely because there is still ''some military activity'' in Botswana and Lesotho and ''perhaps some elements'' in Zimbabwe, although probably not with the knowledge of the Zimbabwean government.
South African sources hint Pretoria's next objective may be to get Angola to reduce its role in supporting the ANC. Angola is widely known to be a major ANC training center, and South African officials are hopeful that current cooperation between Pretoria and Luanda on the Namibian conflict could be parlayed into a broader agreement involving the ANC.
Gains against the ANC in Mozambique and Angola could severely hurt the military wing of the organization, experts say. It was the coming of independence to both countries in 1975 that paved the way for the ANC's rising insurgency over the past seven years.
Tom Lodge, a University of the Witwatersrand political scientist who has studied the ANC, says developments in the region are making the organization's military task ''considerably more difficult.'' But he adds that a lessening of regional support does not come as a total surprise. ''The ANC has anticipated this for some time,'' he says.
Lodge says that for the past several years the ANC has been laying down an infrastructure within South Africa ''for just this eventuality.'' But he concedes this has been difficult and he says it remains to be seen whether the ANC can continue its sabotage campaign internally.
One factor weighing against such a campaign - were it physically possible - might be the ANC's fear it might worsen its relations with neighboring governments. Pretoria may well retaliate against neighboring states for any such attacks, regardless of their origin, experts say.
South African security officials say flatly that the ANC ''does not have any permanent internal infrastructure.''
But even absent any sustained sabotage campaign, the ANC is not likely to disappear.
''The ANC is still the center of gravity of black political sentiment,'' says Lodge. He believes the ANC may now shift its focus to more underground political work in South Africa.
Indeed, although South African security officials deride the ANC as ''the world's least successful terrorist organization,'' they at the same time concede that ''politically the ANC is a growing threat.''
Opinion polls among blacks show the ANC to have broader support than any other political body.
However, transferring the notoriety it has earned by bombing highly visible targets in South Africa - like the Sasol synthetic fuel plants and the Koeberg nuclear power station - into effective political activity will be difficult for the ANC, say analysts.
The ANC was banned by South Africa in 1960, and adopted violence as a tactic in 1961. Pretoria regards the ANC as an extension of the banned South African Communist Party, which it considers ''slavishly'' subservient to Moscow. The ANC regards itself as a bona fide liberation movement born of black dissatisfaction in South Africa, but eager to get support wherever it can, including Moscow.
Greater ANC domestic political activity will be difficult, given South Africa's very stringent security laws and apparatus, experts say. Any new involvement in domestic black politics could also endanger other, legal black groups. Security officials here are already highly suspicious of the emerging black trade union movement. One official alleged the ANC already ''has a foothold and influence'' in certain trade unions.
Groups that have aligned themselves with the same political tradition as the ANC may be in particular danger of state action if the ANC is seen to be expanding its domestic political activity, analysts say.
The United Democratic Front, formed just six months ago, appears particularly vulnerable. The UDF is multiracial and its leading members are supporters of the so-called Freedom Charter - a political document drawn up in 1955 by several political groups including the ANC.
The UDF was launched specifically to oppose Pretoria's new constitution, which will bring Coloreds (persons of mixed-race descent) and Indians into the previously all-white Parliament. Blacks remain excluded.
In its short existence, the UDF has garnered considerable black support as well as steady state harassment. State action could grow firmer. A security official recently described the UDF as ''basically the same as the old Congress Alliance,'' referring to the multiracial alliance of government opponents of the mid-1950s that included the ANC.
The government's constitutional plans appear designed in part to break up the kind of multiracial opposition that the Congress Alliance represented. By bringing Coloreds and Indians into Parliament, Pretoria would hope to give these communities a greater stake in ''the system'' and also broaden its white base of support, close observers say.
Black political opposition to the new constitution appears almost total. But the government has neatly avoided letting this opposition manifest itself. Blacks were hoping they could help influence the majority of Coloreds and Indians to vote ''no'' if the new constitution were put to them in a referendum. But, claiming the Colored and Indian communities did not want a referendum, the government has decided to go straight into parliamentary elections for these communities in August.
Most analysts believe for the foreseeable future it will be difficult for blacks to mount effective legal political opposition internally. Black trade unions are gaining clout. But they are reluctant to get involved in overt political issues for fear of being hammered and thus losing whatever influence they have on behalf of blacks in the economic sphere.
By the same token, observers of black politics say opposition to Pretoria's policies is, if anything, getting more deeply entrenched.
The way most analysts of black politics here see it, blacks are now faced with a doubly difficult challenge. First, blacks must find ways of translating their opposition to Pretoria's policies into tactics that are effective in bringing change. This must be done under very stringent security laws.
Second, blacks must adapt their tactics to a system of government in South Africa that may be no more acceptable to them, but one that has new momentum internally and regionally.
Previous stories were published on March 7 and 8.m