S. Africa signal on nuclear pact suggests it has bomb. But Pretoria has little to gain by move to test or use atomic arms

A surprise diplomatic move by President Pieter Botha suggests to many analysts here that South Africa possesses or will possess atomic weapons, yet has no near-term plans to test or use them. This, at least, is how local analysts view Mr. Botha's recent announcement that South Africa might be willing to sign the Nuclear Non-Proliferation Treaty. The treaty obliges signatories who do not possess nuclear weapons not to develop or acquire them. It also allows the International Atomic Energy Agency (IAEA) to inspect nuclear facilities - to check for diversion of enriched fuels.

That South Africa has the technical capability to produce atomic bombs is beyond question. US officials date this capability to 1981, when Pretoria announced it had produced 45-percent-enriched uranium for a research reactor.

``It is relatively easy to improve forty-five percent enriched uranium to the ninety-percent level needed for weapons,'' notes nuclear-affairs expert Leonard Spector in his book Going Nuclear, published by the Carnegie Endowment for International Peace.

Although Mr. Spector and other experts estimate Pretoria could by now have built up to 18 Hiroshima-size bombs, officials firmly deny it has. And no hard evidence suggests otherwise.

Some analysts see last week's announcement as suggesting South Africa does in fact have an atomic-bomb arsenal, or will before too long. It is hard, they reason, to imagine South Africa - a regional superpower under black-opposition pressure at home, and isolated abroad - would limit itself to a merely theoretical nuclear-weapons capability at the time that it actually moves to sign the pact.

Spector adds that a reported start in the late 1970s on a nuclear-testing facility in the Kalahari Desert, abandoned under US and Soviet pressure, suggests ``South Africa's strong interest in developing'' the bomb.

But analysts here also reason that Botha's announcement signals Pretoria has no plans to test, or use, an atomic weapon in the foreseeable future.

Diplomats have long assumed that political considerations - the danger of alienating generally sympathetic leaders in Washington and London - would militate against the testing of an atomic weapon. Using one was seen as even less likely. In addition to the obvious political fallout, there is clearly a lack of potential targets, since the main threat to Pretoria in recent years has come from inside the country, not from neighbor states.

These assumptions are seen as all the more valid in light of Botha's diplomatic move, and the political atmosphere in which it was made. Domestically, a 15-month-old state of emergency has sharply reduced black anti-government violence. Internationally, the Botha initiative came during an African-led campaign to expel South Africa from the IAEA at its annual meeting in Vienna.

The presumably intended, and ultimately successful, effect of Botha's announcement was to head off this move. The government is clearly reluctant to invite further isolation unnecessarily. Equally important, it knows that it would lose access to world nuclear-energy and industrial technology if ousted from the IAEA.

Even before the Botha announcement, South Africa had allowed IAEA inspections of its nuclear power plant in Koeberg, near Cape Town. But it has declined to allow inspection of its fuel-enrichment and reprocessing facilities in Valindaba and Pelindaba, north of Johannesburg.

Journalists in South Africa operate under official press restrictions.