The South African government appears to be considering major concessions to get a peaceful settlement of the disputes over majority rule in Rhodesia and Namibia (Southwest Africa).

Diplomats and black leaders in Namibia indicate that as the result of new Western pressures:

South Africa apparently opened the door to the possibility of allowing free elections with outside supervision in Namibia in which the rebel movement, the South West Africa People's Orgnization, could participate. This possibility emerged following talks in Cape Town last week between South African officials and representatives of five Western Nations - the U.S., Britain, France, West Germany and Canada.

The sources indicate that the election would be held before independence, scheduled for later next year, in the territory South Africa has administered since 1920 under a League of Nations mandate, which the United Nations and the International Court of Justice subsequently ruled to be illegal.

On Rhodesia, South Africa is apparently now considering an embargo of military fuel supplies if moves are not taken soon to transfer the reins of power from 270,000 whites to Rhodesia's 6.1 million blacks.

There are also unconfirmed reports that the resignation of Rhodesian Prime Minister Ian Smith is included in the deal. the reports say that the resignation would follow a constitutional conference. This is seen as a key factor in proving the Rhodesian government's Smith's resignation sincerity about the transfer of power and in luring militant black nationalists back to the negotiating table.

Both steps, if true, would amount to significant policy changes for South African Prime Minister John Vorster, who has previously denied that his government would ever pressure Rhodesia and claimed that he would not allow the Namibian rebels a role in the transition to majority rule.

The concessions reportedly followed a threat from the Western nations that they would be unable to veto the next U.N. Security Council motion to impose mandatory sanctions on Rhodesia.

Nevertheless, there is still serious doubt whether such gesture by Vorster would be enough and in time. Both would clearly be aimed at helping establish moderate pro-Western black governments and adverting further bloodshed in the two white-ruled countries where campaigns by Marxist-oriented guerillas have escalated in recent months.

But Namibia, it is doubtful that the elections would satisfy the guerrillas especially if called for once an interim government is established under a constitution passed by the Turnhalle conference - a group made up of representatives of Namibia's 11 ethnic groups convened under South African auspices.

The draft constitution stipulates that the legislative body will be divided along ethnic lines. That would give the guerrillas, who are mostly from the dominant Ovambo tribe, minimal say in a new black-dominated government.

Another factor that could antagonize the guerrillas is South Africa's apparent desire to have the election supersised by Western governments, and not by the U.N. as the rebels and the U.N. have both requested.

There could also be problems in Rhodesia with the many rival nationalist factions refusing to cooperate with the new Anglo-American settlement effort despite further concessions by Smith.

Rhodesias' white government may balk. Smith has repeatedly declared that he is not willing to turn over power to a government from which whites are excluded.

Western Diplomats here claim that the South African concessions are not final and no action is expected until after a second round of talks. But there is strong feeling that South Africa is willing to make major moves to try to settle the disputes and avoid new tension in southern Africa.