The South African government and a visiting U.N. delegation apparently have reached a compromise on the implementation of a U.N. peace plan in the Pretoria-run territory of Namibia (Southwest Africa.)

Brian Urquhart, the U.N. under secretary for special political affairs who headed the delegation here, characterized as "helpful" the South African response to proposals to begin implementing the settlement plan. Urquhart received the response just before leaving for New York this evening.

Urquhart refused to disclose details of the apparent compromise, but a source close to the talks indicated that they could lead to an all-party conference hosted by the United Nations to seek an end to the 14-year-old guerrilla war in Nambia between South African forces and black nationalists. g

Such a conference, long favored by South Africa, would bring together Pretoria, the Southwest Africa People's Organization (SWAPO) guerrilla group and probably the political parties favored by South Africa inside Namibia.

In return for such a conference, the South Africans were asked for their agreement to a timetable that would lead to a firm date on which a U.N.-supervised cease-fire would begin in Namibia, the same source said. The agreement would be subject to conditions that involved a demonstration by the United Nations of its impartiality toward all parties that will be contesting the pre-independence elections in Namibia, the source added. Hosting an all-party conference would be one way to make that demonstration.

South Africa has accused the United Nations of favoring SWAPO over the internal parties in Namibia.

Urquhart now faces the sensitive task of convincing the African countries at the United Nations that the South African response to the compromise proposals is enough "progress" to avoid taking punitive action against Pretoria in the form of limited sanctions.

The African countries most closely involved with the U.N. effort to reach a settlement in Namibia were informed last week by U.N. officials of the principal points in the U.N. proposals offered to Pretoria here this week, a source close to the talks said. It is not known, however, whether they were told of the all-party conference proposal.

South Africa favors an all-party conference as a way to get the political parties operating in the territory into a high-profile role in accepting the U.N.-supervised peace plan. This would allow the government to meet accusations from right-wing whites here that it is "forcing" a settlement on whites in Namibia that could hand over power there to a Soviet-armed guerrilla movement.

But Pretoria also values such a conference as a time-gaining exercise during which it hopes the political prestige of its allies in the territory could be bolstered.

The U.S. government and four of its allies have been reluctant to see all-party talks, fearing that South Africa might use them to unravel the peace plan, delay it for a long period or possibly even scuttle it.

At a press conference today, Urquhart emphasized that any U.N. support for such a meeting would depend on the conference's expediting and not delaying implementation of the present U.N. peace plan.