The violent turn of events in southern Africa, "deplored" yesterday in a State Department declaration, has come at a crucial and suspenseful moment in the Reagan administration's drive for diplomatic progress in the region.

State Department officials could only speculate whether there is a connection between several sets of important confidential negotiations, a U.N. Security Council debate that began yesterday and the bloody action and reaction of the past four days.

The "escalating cycle of violence," as the State Department called it, began Friday with the car bombing of South African air force headquarters in Pretoria, for which the African National Congress has claimed responsibility. It continued yesterday with South Africa's retaliatory bombing raid against what Pretoria described as ANC targets in Maputo, the capital of Mozambique.

In its statement, the State Department noted that two ministerial-level meetings between South Africa and Mozambique had been held within the past five months and that the United States had expressed its "willingness to help" search for solutions.

Official sources said that, with U.S. encouragement, the South African-Mozambique talks have covered guidelines or mechanisms to resolve bilateral conflicts. This effort was among the topics in a recent unannounced visit to Washington by Mozambique's minister of security, Jacinto Soares Veloso, the sources said.

The security minister was moved to a post involving foreign trade in a Mozambique governmental shakeup announced Sunday. It was unclear whether this move would affect the Washington-Mozambique dialogue, which has intensified in recent months.

The main business of Veloso's visit here, the sources said, was to assist the confidential discussions between the United States and Angola on the withdrawal of Cuban troops from Angola. Such a Cuban pullout, in the view of Washington and Pretoria, is necessary for success in the long-running effort to bring independence to the South African-ruled territory of Namibia.

As the car bomb was being made ready to shatter the South African air force headquarters, thus touching off a round of sharply increased violence in the region, an important chapter was being written in Moscow in the East-West tug of war over Angola and other radical states in southern Africa.

The visit to the Soviet Union of Angolan President Eduardo dos Santos and his top aides, which ended Friday, was believed to have had a major bearing on whether the Angolans will agree to send the Cubans home and reorient their policy to more workable relations with the West. State Department officials said that they have no reading, yet, on which direction the Moscow talks have taken the southern Africa situation.

The outbreak of bloody violence, according to the State Department sources, is likely to color the atmosphere in which all the confidential contacts are taking place, as well as affect the tone and substance of the public debate over Namibia that began yesterday at the United Nations.

Among the many things not known about the tense southern African situation is whether the large-scale violence will continue and spread, or whether the car bombing and bombing raid will turn out to have been isolated episodes.

What is clear, however, is that many winds are swirling in and around this powder-keg region. What happens in the next few weeks may set a pattern in southern Africa for a long time.