South Africa's troop withdrawal from southern Angola, which the Reagan administration hopes would provide a bridge to Namibian independence, has run into trouble.
Renewed friction with Angola could be a major setback to South Africa's regional detente initiatives and further delay independence for Namibia (South-West Africa), a territory South Africa administers in defiance of the United Nations.
Angola's frustration that South African troops remain in Angola was voiced publicly over the weekend by President Jose Eduardo dos Santos.
In a speech, President dos Santos reportedly said South Africa was failing to meet the withdrawal agreement between the two countries. South African troops should have been out by the end of March, dos Santos said, but one battalion was still 25 miles inside Angolan territory.
Official sources in South Africa concede the troop withdrawal has bogged down in its final phase. But they insist the main reason lies in Angola's failure to keep the South West Africa People's Organization - the guerrilla movement fighting South Africa for control of Namibia - out of the Angolan zone being vacated by South African troops.
SWAPO is again infiltrating Namibia from bases in southern Angola, according to the South African government.
But there is also the strong suggestion that South Africa is using its final withdrawal of troops to lever Angola into a more lasting peace agreement.
One government source said the establishment of a ''longer security arrangement'' would ''facilitate'' the final withdrawal of South African forces.
South Africa would clearly like to freeze SWAPO out of southern Angola permanently.
Pretoria may even have more grandiose plans of seeking some form of nonaggression pact with Angola, along the line of the one signed with Mozambique earlier this year.
Angola is important to South Africa not only because it has offered sanctuary to SWAPO, but also because it is a major training base for African National Congress insurgents. The ANC, banned in South Africa, is waging a sabotage campaign to end white rule in South Africa.
Angola apparently is resisting any long-term cooperation with the South African government in Pretoria.
South Africa made proposals about a lasting security agreement at a meeting on May 21. But informed sources say Angola has not responded to the proposals.
South Africa and Angola signed a withdrawal agreement on Feb. 16 that called for a step-by-step exodus of South African forces from a position of about 120 miles inside Angola.
But Pretoria says a condition of the withdrawal was that neither Cuban nor SWAPO forces be allowed into any of the territory South Africa would vacate.
South African forces have now moved officially to the last post before withdrawing across the border. South African Foreign Minister Roelof Botha said almost four weeks ago that the withdrawal would be finished in ''a matter of days.''
But since arriving at Ngiva, the last position before crossing the border, Pretoria claims SWAPO infiltrations have again become serious.
''All the delays are because of violations by SWAPO,'' said a South African government source.
This source said South Africa was happy with the cooperation it has had with Angola in the so-called ''joint monitoring commission,'' the body established to jointly monitor the terms of the withdrawal agreement.
But the source questioned whether the Angolan government in Luanda was applying sufficient political pressure on SWAPO insurgents to keep them out of the border zone.