The birth of Zimbabwe this month poses a new and major challenge for the United States in the heart of one of the world's richest and most strategic regions. Should Washington embrace and support a former black guerrilla chieftain who won a landslide election victory under the banner of Marxism?

The answer is yes, according to senior U.S. officials dealing with Africa. By doing so, they say privately, the United States would be seizing a unique opportunity to help direct the future of southern Africa away from racial confrontation and toward a democratic development.

After seven years of war between Rhodesia's white-minority government and black nationalist insurgents, the victory of one of guerrilla leaders, Robert Mugabe, a self-described Marxist, initially stunned the whites in Rhodesia and neighboring South Africa, as well as their friends in the west.

But Mugabe has managed to surprise both his friends and foes. During the last month, the new prime minister largely dropped Marxist rhetoric as he formed a government representative of various views and both races. While he reaffirmed his intention to correct past political and economic injustices suffered by blacks, he said he would do so without creating injustices against the white minority. Finally, he has signaled willingness to cooperate with the West.

Is Mugabe, for reasons of tactics and politics, merely masking his true intentions, as critics such as Sen. Jesse Helms (R-N.C.) maintain? Or is he a "nationalist first, Marxist second" and, as such, unlikely to become a Soviet puppet, as some U.S. officials who know Mugabe contend?

These questions touch the very core of an ongoing foreign policy debate here.

Former secretary of state Henry Kissinger, who consistently has criticized the Carter administration's policies as encourageing radical trends in the Third World, raised the fundamental question again in a speech here last week.

"Are we identifying with the wave of the future, or are we abetting our own progressive isolation and irrelevance?" Kissinger asked.

Before last month's Rhodesian election, Kissinger described Carter's approach to Rhodesia as one of trying to win over Mugabe by co-opting his radical program. This, he said, "dooms us to chasing a mirage" because the leftist radicals are "usually anti-U.S., almost always anticapitalist."

But rapid changes in Zimbabwe have left Kissinger speechless and he concentrated this week on other countries while assailing the Carter administration for encouraging "the radical tide and communist proxy intervention." He had no comment when asked specifically about Zimbabwe developments.

Administration officials maintain brace and support a former black majority rule in Rhodesia is a major diplomatic coup because it has effectively shut out the Soviets and Cubans from southern Africa.

Beyond that, these officials say, the evolution of the new Zimbabwe state is now providing "tremendous opportunities for us" to influence events in the entire region.

Zimbabwe is at a crossroads, linking transportation routes from Zaire to South Africa and from Angola to Mozambique. Its evolution will undoubtedly influence the Marxist governments of Mozambique and Angola as much as white ruled South Africa and Namibia (Southwest Africa).

The Carter administration has decided to extend "quickly and conclusively" its support to Mugabe in an effort to "demonstrate to him that Zimbabwe's future lies with the West," according to U.S. officials. They expect the United States to offer Zimbabwe an economic aid package of about $14 million.

But these officials privately suggest that the United States should put together a more significant aid package -- "at least $40 million this year," one senior official said -- to help restore the country's economy.

Washington's objectives are two-fold. On one hand, the peaceful evolution of biracial democracy in Zimbabwe holds out the prospect of a similar development in Namibia, which is currently under South Africa's control, and of eventual white-black dialogue in South Africa itself.

If Mugabe is successful, one senior official said, "the South African whites may get down to serious talking with their own black leaders on grounds that it was better to negotiate with them than fight them."

Zimbabwe's successful development, on the other hand, would tend to reduce Moscow's influence in Mozambique and Angola, where leftist governments have shown signs of disenchantment with Soviet-style policies they had adopted.

Both Angola and Mozambique supported the diplomatic settlement of the Rhodesian issue. In particular, Mozambique's President Samora Machel has counseled Mugabe against a Soviet-style, planned economy. Machel recently decided to relinquish government ownership of small enterprises and services.

In an interview with Robert MacNeil and Jim Lehrer of PBS-TV, Mugabe said recently that he had "derived certain principles from Marxism and Leninism." But, he said, "we have also derived definitely Christian principles and principles from our own tradition. A blend of the three makes our own socialist outlook."

For the moment, Mugabe is a conciliator. He has signaled willingness to work with the West, and he has no ties with the Soviets, who supported Joshua Nkomo's guerrilla faction during the war. Mugabe received some support from China and Yugoslavia, but he is regarded very much as being his own man.

But U.S. Officials say that if the West displays hostility toward his government or fails to come to its aid, Mugabe would not hesitate to seek help from the Soviet Bloc countries. Such a decision would come soon after he comes to grips with the formidable task of implementing his campaign promises about jobs, land, health services, wages and housing.

Because of Zimbabwe's economic and transportation links with South Africa, it is regarded as essential that the South Africans indicate their confidence in Mugabe rather than seek to destabilize the new government.

In simple terms, this means that the Carter administration expects the South Africans to maintain their normal trade and communication links with Zimbabwe without asking for unacceptable political concessions.

Mugabe has to maintain his ideological opposition to apartheid, U.S. officials said. His victory in a free election is perceived by black Africa as a demonstration of the inevitability of black-majority rule.

But, the officials said, Mugabe's victory also holds out the hope of a peaceful transition -- an alternative to armed struggle as well as an evolution toward racial conciliation.