Within a day of South Africa's announcement that nearly all issues holding up a Namibian settlement had been resolved in talks with U.N. Secretary General Javier Perez de Cuellar, the main political group Pretoria backs in the disputed territory sought to revive one of them.

Dirk Mudge, chairman of the Democratic Turnhalle Alliance, an association of 11 ethnically based parties, announced that his group still regards the United Nations as biased in favor of the black nationalist South-West Africa People's Organization (SWAPO) and will not participate in pre-independence elections unless the international organization demonstrates its impartiality.

The alliance thus repeated a threat it made at a conference in Geneva in 1980, after initiatives led by the Carter administration appeared to have brought the Namibian issue close to agreement.

The objection was based on General Assembly resolutions recognizing SWAPO as "the sole authentic voice of the people of Namibia." South Africa, which had not raised the question of U.N. impartiality in the negotiations until then, backed Mudge, and the settlement prospects collapsed.

The negotiations were resumed by the Reagan administration and have advanced again gradually. They appeared to have reached a point one step away from agreement after two days of talks between South African officials and Perez de Cuellar. South African Foreign Minister Pik Botha announced that all outstanding issues had been resolved, except for the South African--and U.S.--insistence that Cuban troops must leave neighboring Angola first. Botha specified that the question of impartiality was "no longer an issue."

Nico Bessinger, spokesman for a group of internally based SWAPO leaders, acknowledged that the talks had achieved useful progress and said there were no obstructions to a settlement as far as the nationalist movement was concerned.

Perez de Cuellar, in an effort to demonstrate impartiality, risked controversy by allowing his South African hosts to fly him to the war zone of northern Namibia. He returned to Windhoek today to begin a public show of trying to see the leaders of all the main internal political parties.

This is no easy task. Although Namibia has a population of fewer than 1 million, it has more than 40 political parties--of which 17, counting the alliance as one, can be regarded as having some substance. Perez de Cuellar's aides calculated that he could spare only 15 minutes for each party. The Democratic Alliance chose to interpret the short notice and brief time allocation as evidence of continuing U.N. bias and its leaders refused to see Perez de Cuellar.

"I am sure Sam Nujoma the exiled SWAPO leader whom Perez de Cuellar is to meet in Luanda, Angola, Friday was given notice weeks ago and will have all the time he wants," Mudge told a press conference.

Confirming that the alliance still regarded the impartiality issue as alive, Mudge said his parties would not participate in elections that are not free and fair, and they cannot be fair "if the umpire has recognized one of the teams as the winner in advance."