The agreement reached Wednesday in the Angolan capital of Luanda between militant Namibian nationalists and five Western powers represents a major diplomatic victory for the West and a breakthrough in its search for negotiated settlements to the burning racial conflicts of southern Africa.

For the first time, there is now some hope that the deteriorating situation throughout this tense region of the continent, scarred by escalating warfare and dotted by massacres of blacks and whites, can be halted and even reversed.

With an internationally acceptable solution to the Namibia dispute now in sight, one of the first consequences of the accord will be to isolate further Rhodesia's recalcitrant transitional government and perhaps force it now to attend a Western-sponsored general peace conference with its guerrilla adversaries.

For the Soviet Union, the accord can only be a blow to its hopes for increasing its influence in this region through the backing of guerrilla warfare at the West's expense, for it has brought closely together the five major Western powers and the five socalled front-line African states, including the two Marxist ones in Angola and Mozambique, in a combined diplomatic offensive that has finally borne fruit.

The front-line states, whose chairman is Tanzanian President Julius K. Nyerere, played a crucial role in pressuring the Southwest African People's Organization (SWAPO) into accepting the Western plan despite SWAPO's strong objections to several key provisions. Nyerere was reported yesterday to be delighted upon hearing of the agreement.

The same front-line approach toward the nationalist guerrillas in Rhodesia, plus increased South African pressure on the transitional government there, could well now lead to some progress on the deadlocked British-American peace plan for that war-exhausted country, though the situation there remains for more complex.

There is still a rocky road ahead in Namibia for the Western plan. South Africa regards SWAPO president Sam Nujoma as an ouright "communist," while the Namibian nationalists are convinced the South Africans are out to do them in at the elections.

The agreement is a major personal triumph for U.S. Ambassador Donald McHenry, who for 15 months has practiced a unique style of quiet diplomacy, persisting in his unthanked efforts despite multiple obstacles, repeated stebacks and dire threats from both South Africa and the Namibian nationalists.

McHenry has served as chairman of the so-called Western "contact group" made up of the United States, Britain, France, Canada and West Germany.

The Western proposals provide for United Nations. Supervised elections for a constituent assembly in Namibia at which a new constitution will be drawn up. The assembly would also prepare the country for its independence under a black majority government by the end of this year.

About 5,000 U.N. soldiers and 1,000 administrative personnel are to be brought into the country to supervise the transition period jointly with the South African-appointed administrator general, justice Martinus Steyn.

South Africa is to withdraw all but 1,500 of its more than 20,000 troops now stationed in Namibia before elections are held and then the remainder one week after a U.N. certification of the results.

The South Africans had insisted upon the right to keep those last 1,500 troops in northern Namibia while SWAPO was demanding they be removed to the far south. It appears the Namibian nationalists were forced to give in to the South African position on this issue at Luanda.

Another key sticking point was the status of Namibia's only deep water port, Walvis Bay, which South Africa insists is a part of its own republic historically and legally. SWAPO is reported to have accepted a formula under which the five Western powers and the U.N. Security Council will recognize Walvis Bay as an integral part of Namibia despite the South African claim to it.

The issue however will be left to later negotiations between South Africa and an independent Namibian government.

South Africa has been ruling the mineral-rich but sparsely inhabited former German colony since the end of World War I under an old League of Nations mandate. But in 1966, the United Nations ceased to recognize this mandate and began demanding that South Africa give the territory independence.

After more than a year of periodic negotiations, South Africa agreed to the Western plan in late April, but the Namibian nationalist organization broke off talks with the five Western powers after a South Africa raid May 5 at one of their refugee and guerrilla camps in southern Angola, in which around 800 persons were killed.

Swapo then began hardening its demands to include a revamping of the police force in Namibia as well as insisting on South African acceptance of Walvis Bay as part of Namibia before its independence and the removal of all South African troops to the southern part of Namibia.

But a summit of the Frontline states in early June in Luanda broke the impasse and led to their decision to force SWAPO into dropping its demands.

With South Africa now committed to a Western-backed plan involving the deployment of a U.N. peacekeeping force, it is though possible here that Pretoria may now be willing to step up pressure on Rhodesia's transitional government to negotiate a similar internationally acceptable solution there.

The Tanzanian theory is that South Africa can ill-afford to back an internal settlement in Rhodesia, such as is being tried now, once it has accepted a totally different approach to Namibia. This view is shared by many American and other Western diplomats in the region.

However, South African Prime Minister John Vorster has publicly come out in support of the new biracial transitional government in Rhodesia and even criticized the United States and other Western countries for not doing the same.

The Patriotic Front, representing guerrillas now fighting in Rhodesia, has appeared to have adopted a position lately that there is little need to negotiate since it is apparently winning against the transitional government. But the frontline states, which have supported the British-American peace plan, could, if they wished, force the guerrillas to take the diplomatic route. These states supply most of the guerrillas' African backing, especially Zambia and Mozambique, from which the guerrillas operate.

The agreement in Luanda has come after months of tedious negotiations.

The agreement in Luanda has come after months of tedious negotiations.

McHenry, as the Western group's chairman, traveled tens of thousands of miles between New York, where he is deputy head of the U.S. Mission to the United Nations, and seven African capitals. At times he was on the road a month or six weeks at a stretch crisscrossing the continent. Much of the time was spent tracking down SWAPO president Nujoma, possibly the most slippery nationalist leader the West has to deal with in Southern Africa.

South African provocations and threats to "go it alone" were another major hazard along the way, but McHenry was once heard to remark in a State of exhaustion in Lusaka," I've got more patience than they have and I'm going to outlast them all until they agree."