Saudi Arabia, America's most important ally in the Red Sea region and increasingly throughout Africa, is becoming one of the sharpest overseas critics of what it regards as the Carter administration's policy of courting favor with black Africa by refusing to meet head on the growing Soviet-Cuban challenge.

As the Saudis see it, the Soviet Union has now established its clear intention of interventing wherever possible all over Africa and the surrounding region. This, they make clear in their mild-mannered, soft-spoken way, is a direct threat to the Saudi kingdowm that cannot be dealt with merely by verbal protests from Washington.

"It has been shown that this thing grows," said Saudi Foreign Minister Prince Saud Faisal in a recent interview, referring to Soviet and Cuban intervention in various African countries. "When Angola came, it was said to be a unique situation. But it repeated itself in Zaire and in Ethiopia. So it does spread."

The recent coup in Afghanistan resulting in the establishment of a Communist-dominated government there, has only served to confirm the Saudis' worst fears about Soviet intentions. With thousands of Cuban troops present just across the Red Sea in Ethiopia and a strong Soviet-Cuban presence is a growing sense of encirclement here.

All this helps to explain why the Saudis are pressing the Carter administration to adopt a more aggressive posture in Africa, including an increase in military assistance to moderate Arab and black African states, and even hinting at the need for a direct American intervention to counter the expanding Soviet-Cuban military presence. At this point, it appears that Saudi Arabia distributes more aid in black Africa than the United States.

The real issue, according to Prince Saud, is not the Carter administration's policy of nonintervention, but whether the Soviet policy of repeated massive involvement in the internal affairs of African countries, and even intra-African crises, will go on unchallenged.

Saudi Arabia is rich in oil and dollars and the situation "is not a financial problem," remarked Prince Saud, who describes his kingdom as a "small country" of limited defense means. Something more than verbal protest from the United States has become "a necessity," he added.

The Saudis are stepping up their financial assistance to pro-Western African states threatened by the escalating Soviet-Cuban presence in Africa. It is not known by outsiders here exactly how much of the estimated $6.5 billion Saudi Arabia distributed in aid last year was earmarked for African countries.

It is likely however, that the amount easily surpassed the $350 million given out by the United States, making the Saudis an important asset in American efforts to stem the Soviet-Cuban tide on the continent.

There is a notable irony in the new Saudi activist role in Africa and Saudi complaints about American passivity toward Soviet-Cuban challenge. Only a few years ago, the Nixon-Ford administration was pushing a somewhat lethargic Saudi government to do more to help the West contain the spread of Communist influence on the Arabian Peninsula. Now, it is the Saudis who are pressing the Carter administration on the same point in both Africa and the Red Sea region.

With the United States increasingly dependent on Saudi oil and backing for the besieged dollar, Washington can no longer afford to irgnore the pressure from Riyadh. But it has placed the Carter administration in the difficult position of having to recocile the demands of its new black African allies with those of its most important Arab oil partners.

While these Arab states tend to view Africa mainly as a new Cold War theater and the soft underbelly to their own exposed lands, much of black Africa is preoccupied now with the problem of containing local forces threatening the national unity of various countries and that of ending white rule in southern Africa. On Both accounts, the Soviets and Cubans have suddenly emerged as black Africa's most important allies.

The growing disagreement between Washington and Riyadh over the Carter administration's new Africa policy came to a head last year over the U.S. refusal to provide Somalia with arms after President Mohammed Siad Barre cut most of his ties to the Soviet Union and broke relations with Cuba.

The Saudis had been encouraging the United States to do more to wean Somalia away from the Soviet Bloc for years before the Somali-Ethiopian war led to Siad Barre's break with Moscow. They were deeply disappointed when the split came and there was no "positive answer" from Washington, as Prince Saud put it.

But Washington found itself under enormous pressure from its black African allies not to reward Somalia because it was regarded as a flagrant violator of Ethiopia's borders. Pro-Western Kenya, another neighbor fearing Somalia's territorial ambitions, was particularly insistent that the Carter administration reject Somalia's request for military assistance.

Meanwhile, the malaise in the special Saudi-American relationship is deepening over the lack of a strong U.S. response to the expanding Soviet-Cuban presence in the Red Sea region. It is exacerbated as the number of Cuban troops increases just across that strategic waterway in Ethiopia's northern war-torn Eritrea Province.

"It is in principle a threat to the independence and security of our region and directly a threat to the independence and security of our country," remarded Prince Saud. "What conceivable basis would they have for intervening in that area?"

For the Saudis, the primary issue at stake in Ethiopia is not the preservation of its territorial integrity against a separatist movement, which is the view most black African nations hold and have impressed on the Carter administration. Rather, it is in the Saudi view the massive intervention of the Soviet Union in the internal affairs of an African country, this time one that could easily serve as a springboard into the Arabian Peninsula.

As a first step, the Saudis clearly want the Carter administration to step up their military assistance to moderate African and Arab countries with Soviet-backed neighbors, such as Kenya, Zaire and Sudan.

"If threatened countries are left alone, then there is not hope," said Prince Saud. "If they are not given arms even when they want to fight, if they are not given the opportunity to do so, then we are really in a hopeless situation."

The Saudis seem to be convinced that the next arena for a major Soviet intervention will be southern Africa. Saudi Arabia has just agreed to open an embassy in the Zambian capital of Lusaka and will probably provide financial assistance to that economically hard pressed country.

Saudi Arabia is also providing millions of dollars to the special $12 million dollar Arab fund in support of the Rhodesian nationalist Patriotic Front, apparently hoping to offset Soviet and Cuban influence inside the guerrilla alliance. There are also reports in Salisbury that Arab money is going to the new biracial Rhodesian government, although it is not clear which countries are supplying it.

The Saudis are also financing Sudanese and Egyptian arms purchases in the West, the Moroccan and Mauritanian war against the Soviet-backed Polisario liberation movement in the old Spanish Sahara, and various pro-Western African states, like Zaire, that are now in desperate financial straits.