There are increasing signs that South Africa is nearing a decision to attempt its own internal settlement in Namibia following the new sympathy being shown in Washington and London toward a similar solution to the Rhodesian conflict and a sharp upsurge of fighting in the South African-administered territory.

Western sources here said fears that South Africa was about to announce a date for its own elections in Namibia spurred vigorous diplomatic efforts last week to persuade Pretoria to wait, pending another Western effort in the next few days to break the deadlock in negotiations for an internationally acceptable accord leading to Namibian independence.

South Africa appears to be encouraged to take such a step by reports of growing disenchantment with the guerrilla activities, and increasingly pro-Marxist slant, of the militant black nationalist Southwest African People's Organization (SWAPO) among its supporters in the powerful Protestant and Catholic churches.

In addition, the South African government is under mounting pressure from both black and white leaders inside Namibia to proceed with its own settlement.

South Africa has administered Namibia, otherwise known as Southwest Africa, since the grant of a mandate over the former German colony by the old League of Nations at the end of World War I. Last year, it held a constitutional conference of representatives from the 11 different ethnic groups living in the territory to prepare for independence by the end of this year.

However, SWAPO, which is recognized by the United Nations as the only genuine representative of all the Namibian people, refused to attend because the conference was held on basis of ethnic representation. Instead, it stepped up training of guerrillas with Soviet and Cuban backing at camps in southern Angola.

The clearest indication yet of this country's growing inclination to go it alone even at the risk of economic sanctions came Friday when Foreign Minister Roelof Botha told Parliament that "It is not at all certain --indeed it looks to be unlikely -- that an internationally acceptable solution will be reached."

"I want to say here today that we may get possible sanctions, that pressure on us will increase and that an escalation of violence may come in southern Africa." he added.

Botha said South Africa would continue to "lean over backwards" to reach an internationally acceptable solution through its ongoing talks with the five Western powers. But the thrust of his statement seemed primarily aimed at preparing South African and world opinion for a possible decision by Pretoria to go ahead with its own plan for holding elections and unilaterally granting Namibia independence by the end of this year.

Earlier in the week, Botha traveled to the Namibian capital of Windhoek to discuss "other alternatives" to the Western proposals with local white and black leaders.

A delegation of these internal leaders had just returned from a secret mission to Western Europe, where they held talks on the possible foreign recognition of a Namibian government headed by the South African-backed Democratic Turnalle Alliance. The delegation's leader, Dirk Mudge, described himself as "satisfied" with the results of the mission but refused to disclose with whom it had met.

A South African decision to opt for its own settlement would almost certainly escalate the guerrilla war being waged by SWAPO, which rejects this approach.

South African appears to be increasingly willing to run this risk rather than allow SWAPO to take over the mineral-rich territory populated by only about one million people. "We cannot allow the territory to fall into the hands of Marxist tyranny," Botha told parliament.

Western diplomatic sources ascribe the changing South African attitude partly to statements in London and Washington over the past two weeks suggesting that the two Western powwers are now more favorably disposed towards Rhodesian Prime Minister Ian Smith's effort to work out his own internal settlement with three moderate black leaders based inside Rhodesia.

"The South Africans are looking carefully at the Rhodesian situation to see what the West is going to do," said one Western diplomat.

Britain and the United States have been holding separate negotiations with the militant Patriotic Front, the externally based guerrilla alliance that has rejected Smith's negotiations.

The South Africans seem to reason that if the two Western powers now swing away from the Patriotic Front and back an internal settlement in Rhodesia, there is a good chance they will take a similar attitude toward a South African-sponsored solution to the Namibian constitutional dispute.

The other factor in South African thinking about Namibia is said to be the sharp upsurge in SWAPO's guerrilla war. In the past week, several south African soldiers have been killed and one captured by SWAPO guerrillas in clashes in northern Namibia.

On Tuesday, 80 SWAPO guerrillas took more than 200 youths from an Anglican mission school across the border into Angola. South African authorities said they had been "abducted" but SWAPO and church sources in Namibia said they had gone willingly.

The size of the SWAPO guerrila groups operating inside Namibia and the death of so many South Africans in just one week appeared to indicate that the war there is taking a sharp turn.

This development is likely to harden the South African position toward the Western proposal for a Namiban settlement based on elections in which SWAPO would participate. The United Nations would monitor the activities of both South African and SWAPO military forces.

The United States, Britain, West Germany, France and Canada have been holding periodic talks over the past year with South Africa in the search for a settlement of the constitutional dispute.

The deadlock between South Africa and SWAPO led the five Western powers to intervene as mediators. These negotiations have narrowed differences to three main issues: the number and location of South African troops remaining in the territory during elections; the role and size of a proposed U.N. peacekeeping force, and the powers of the South African-appointed administrator general and the U.N. appointed special representative in Namibia.