Black and white leaders in Rhodesia have now set in motion a course of events that has a better than even chance of touching off the worst civil war in southern Africa's history, with a high potential for again drawing in all the outside forces that confronted each other in the Angolan conflict.

While no one here is giving very good odds on the survival of the new multiracial transitional government set up this week, most seem ready to bet heavily tht the worst fighting in the six-year-old guerrilla war - which has already taken up to 9,000 lives - is about to break out. In addition, it is now taking on the character of a black-against-black struggle for power.

At stake is not only which black faction will rule the new Zimbabwe, but whether this minerally and agriculturally rich land will be socialist or capitalist, Eastern or Western, in orientation.

The war clouds are already thickening. Hundreds of nationlist guerrillas are pouring in from Mozambique and Zambia to do battle against the transitional government. There are unconfirmed Rhodesian and South African reports of a new major buildup of Soviet arms and Cuban personnel in Mozambique, and the first indications that South Africa may be ready to step up its military assistance to Rhodesia.

The United States and Britain have launched an 11th hour diplomatic offensive to persuade all of Rhodesia's warring and rival parties to attend one last peace conference. But none has shown interest, leaving the African "front-line" states and south Africa as the West's last hope for forcing a meeting of the nationalist leaders in the transition government and those outside the country.

This explains a sudden front-line summit meeting in Dar es Salaam announced for this weekend. The meeting was called after Tanzanian President Julius Nyerere met Tuesday with U.S. Ambassador Andrew Young, who is leading the Western peace initiative in southern Africa now and wants to use the occasion to meet informally with the five front-line presidents.

Meanwhile, the transitional government, under the combined leadership of white Prime Minister Ian Smith and three locally based black leaders, is about to launch a major campaign to win the hearts and minds of the 10,000 to 20,000 guerrillas fighting under the banner of the externally based Patriotic Front.

If the campaign succeeds, or even half succeds, the transitional government should give birth to full black majority rule at the end of this year, almost certainly under the moderate pro-Western leadership of Bishop Abel Muzorewa.

Much now depends on this Methodist bishop, whose past political record of indecision and hiding in the face of crisis is the cause of much concern among his black and white supporters today.A respected religious and political leaders among the Shona peoples, who make up more than 80 percent of Rhodesia's 6.7 million blacks, Muzorewa, 52, is the only one of the three black signers of the agreement here with a proven national following of major scope. He has repeatedly brought out crowds of 100,000 or more at his homecoming rallies.

Whether the soft-spoken prelate can rise to the challenge of leadership at this time of national crisis is a question many Rhodesians are pondering. In his favor, observers note a new self-confidence, determination and ability to articulate his views since his commitment to the internal settlement. White Rhodesian officials were greatly encouraged by the way he stood up to British and American pressures during his recent trip to London and Washington.

Like the bishop's uncertain leadership abilities, the about-to-be-launched "hearts and minds" campaign aimed at the guerrillas is a subject of constant debate in Salisbury. Both the bishop and the Rev. Ndabanningi Sithole, another signer of the March 3 Salisbury agreement, talk with great confidence in public of their ability to command the guerrillas to lay down their arms and come home.

Sithole, who still claims leadership over one of the two guerrilla armies making up the Patriotic Front, has just visited the eastern border where the war is hottest. He said at a press conference Wednesday that some guerrilla commanders had contacted him there and expressed their support for the internal settlement.

But resident foreign correspondents here and many other outside observers express the gravest doubts about the ability of either Sithole or Bishop Muzorewa to win over enough of the guerrillas to make a significant difference. The bishop is reported to have admitted during negotiations with Smiths in early February that his control over the guerrillas was minimal.

So far, there is no sign that the 6,000 guerrillas estimated to be inside the country now are ready to defect to the transitional government. However, the general amnesty and "GI bills of rights" promised for returning guerrillas have not yet been formally announced and until they are the guerrialls' true allegiance cannot be judged accurately.

Similarly, it is difficult to assess the real strength of the three locally based black leaders today, although it is clear that only Muzorewa can still draw large crowds. Last Sunday, perhaps 150,000 turned out to welcome him back home. This was a somewhat smaller turnout to the previous ones, but it still appeared to show that the biship commands the support of a majority of the capital's black population and, perhaps most significantly, of much of its youth. There were thousands of teenagers in the throng.

Outside' the capital, heavily populated by shona people, Muzorewa's popularity is less certain. A recent public opinion poll, conducted by the South African Argus news service in south central Rhodesia, showed that 55 per cent of those questioned (about 120) supported the bishop and just under 20 percent supported Joshua Nkomo, the Soviet and Cuban-backed co-leader of the Patriotic Front.

The two towns and single tribal trust land where the poll was taken were in a region inhabited by both the Shona and Ndebele populations. The other two internal nationalist leaders, Sithole and Chief Jeremiah Chirau, as well as Robert Mugabe, the other Patriotic Front leader, ran far behind.

But a steadily increasing proportion of the country, a third or more of which is already under strong Patriotic Front influence, is coming within the sphere os guerrilla activities. It is now widely believed that even the black townships around Salisbury are heavily infiltrated with guerrillas bold engouh to take time out there from the rigors of the bush.

In addition, there are thousands of freshly trained guerrillas, belonging to Nkomo's Ndebele-based Zimbabwe African People's Union (ZAPU), now joining the battle. Oberservers here see little reason for the Ndebeles traditional warriors, to lay down their arms when the transitional government is dominated by Shona leaders.

Furthermore, Muzorewa bitterly attacked Nkomo at the rally here last Sunday and as his Shona supporters were heading homeward they could be heard singing anti-Nkomo songs with great gusto. By contrast, the bishop spoke not a single disparaging word against Mugabe, a Shona leader like himself.

This tactie undoubtedly helps to consolidate Muzorewa's popularity among the Shona. It must help just as certainly to stir up tribal hatreds and thus promote increased tension between the two wings of the Patriotic Front, one of which is mostly Shona and the other Ndebele.

But it augurs poorly for creating conditions that might lure Nkomo's more than 10,000 guerrillas into laying down their arms and backing the internal settlement. It can only help to establish an atmosphere in which civil war will blossom, with the strong likelihood that the Soviets and Cubans will become involved in helping Nkomo.

Nkomo, aside from receiving Soviet weapons and Cuban instructors, also has the political backing of the Soviet Union, which has denounced the Salisbury settlement. Nkomo's faction has trained in Angola and Zambia.

The more militant Zimbabwe National Union, taining guerrillas in Mozambique, has been backed by China.