South Africa-Mozambique pact: a diplomatic plum for Pretoria?

Today's signing of a nonaggression pact between South Africa and Mozambique gives Pretoria something it has long sought: a foot in the door toward better relations with black-ruled Africa.

More important, Pretoria views an accommodation with its black-ruled neighbors as the first step on the road to better relations with the West in general, say political analysts here.

Broadly, the accord between the two nations pledges each not to let its territory be used by rebel movements against the other. It also precludes the use of a third state for such acts and establishes a joint commission to ensure the terms of the agreement are met by both sides.

The surprise is that in signing the agreement, Pretoria has opened a wedge without making any concessions on its domestic policy of apartheid. In the past, most black-ruled states made such reforms a precondition to closer ties. Pretoria has been able to bypass this condition by exerting its military and economic dominance in the region.

The stage now appears set for the clash of two opposing strategies, analysts say:

* Pretoria will try to move forward with its regional detente in hopes of breaching its international isolation, without compromising white rule within South Africa.

* The West and the black-ruled states will attempt to extract concessions from a more outward-looking South Africa that ultimately would have to include a political accommodation of South Africa's black majority.

While the West and the leaders of Africa have said South Africa's peace moves will ultimately succeed only if they include concessions on apartheid, observers here believe South Africa has assembled enough bargaining chips to marginally improve its position - both regionally and internationally - for some time without making major domestic concessions.

The nonaggression pact with Mozambique - the first between South Africa and a black-ruled state - is evidence of South Africa's bargaining strength.

Since coming to power in 1975, the Marxist rulers of Mozambique have been among South Africa's most implacable foes. But Pretoria has rendered the Mozambique government almost helpless with widely acknowledged aid to the Mozambican National Resistance (MNR), a rebel movement fighting the Marxist government in Maputo, and manipulation of Mozambique's heavy economic dependence on South Africa.

Maputo effectively sent up the white flag last year when President Samora Machel sought Western aid and signaled he was ready for a reapproachment with Pretoria. The Americans and the Portuguese worked behind the scenes to make the dialogue possible.

In narrower terms, the Accord of Nkomati, as the nonagression pact is known, gives South Africa a major strategic victory. Pretoria claims the vast majority of sabotage attacks by the banned African National Congress (ANC) originate in Mozambique. Under the terms of the agreement, Mozambique will no longer allow the ANC to operate militarily from its soil. No other state bordering South Africa permits the ANC to operate militarily from their territory.

Pretoria will apparently end its support for the MNR. This could have direct economic benefit for Mozambique which declared recently in seeking to renegotiate some international loans that South Africa's ''undeclared war '' had cost Maputo close to $4 billion since independence.

Mozambique's shrinking economy has been particularly hard hit recently by drought, which has reportedly sent tens of thousands of refugees fleeing to neighboring Zimbabwe in search of food.

After signing the agreement in an elegant railroad car in the subtropical border region near Komatipoort, Pretoria is expected to press its regional initiative elsewhere, leading eventually to negotiations for the independence of Namibia.