How would the current South African government have voted had it been one of the 11 members of the U.N. Security Council debating Resolution 191 in June 1964?

Would it have sided with the majority of eight who imposed an arms embargo against the apartheid leaders who ruled Pretoria at the time, setting in motion a worldwide boycott of their racist regime? Or would it have joined the Soviet Union, Czechoslovakia, and France, who abstained? Would it have gone even further, using legalistic arguments to push the Soviets to veto the resolution outright?

The question is not only a what-if historical exercise. South Africa, which in January joined the Security Council, has become a powerful voice on that panel, which now has 15 members. Next month, Pretoria will assume the rotating presidency, putting it in a position to set the tone as the council’s debate on Iran heats up.

Tomorrow, the United Nations’ own nuclear watchdog will tell council members what they already know: defying resolutions, the mullahs have not suspended uranium enrichment. China, Russia, and South Africa are expected to lead the fight against any meaningful reaction to this defiance.

For South Africa, the alliance with Russia and China, which oppose interference in the internal affairs of wayward regimes, is a historical lesson in political cynicism. Remember apartheid? Remember Nelson Mandela?

This January, in South Africa’s first significant vote as a council member, it helped to block a mild, non-binding resolution of rebuke to a regime that had long-imprisoned a freedom-aspiring opposition leader, and to a group in power that cruelly oppresses another, disenfranchised group.

Pretoria’s ambassador at the United Nations, Dumisani Kumalo, joined his Chinese and Russian colleagues who vetoed a British-American proposal to reprimand the ruling junta in Burma. The junta’s record of rape and killings of its Karen-speaking minority, and its imprisonment of the world-renowned opposition leader Aung San Suu Kyi, have led some to compare it to South Africa’s apartheid rulers.

The comparison was heard loudest in Pretoria itself. “Will South Africa ever meet a dictator it does not like?” asked a leader of the largest opposition party, the Democratic Alliance’s Douglas Gibson. “I am deeply disappointed,” said Archbishop Desmond Tutu. Burma’s “tyrannical military regime is gloating, and we sided with them.” Stung by the criticism, Mr. Kumalo resorted to U.N. legalisms. “It’s very important that the Security Council does what the charter says it’s supposed to do, which is maintain international peace and security,” he said last week, when I asked him about the historical comparison.

“In the case of South Africa, we had an apartheid regime that was a menace to its neighbors,” he argued. “They bombed and killed people — in Zimbabwe, in Botswana, in Lesotho.” In contrast, Burma “is not bombing India, they’re not bombing Malaysia.”

Mr. Kumalo, a former exiled reporter and organizer of divestment campaigns in America against his apartheid tormentors, now argues that the Security Council acted then only because of South Africa’s external aggression. Cases of internal oppression, like in today’s Burma, should instead be handled by human rights organs, he told me.

Good luck. The Geneva-based U.N. Human Rights Council is intersted only in condemning Israel, which it has already done eight times. The only attempt to condemn another country, Sudan, was blocked after Khartoum last week once more rejected a Geneva-mandated fact finding mission.

And no, that 1964 resolution, in which the council decided to impose sanctions against Pretoria, had nothing to do with aggression against neighbors. It came as a direct reaction to the life sentence imposed on Mr. Mandela. One paragraph appealed to the regime to “liberate all persons imprisoned, interned, or subjected to other restrictions for having opposed the policies of apartheid.” By Mr. Kumalo’s logic, the menace presented by Tehran to the entire Middle East should lead to Security Council sanctions, while anti-apartheid resolutions should have been sent to Geneva, where they would wait their turn — after the 50th anti-Israel resolution perhaps. But Pretoria, as it did on Burma, most likely will now side with China and Russia in opposing any meaningful action against Iran — or any other world tyrant for that matter.

South Africa is now a top continental power, harboring even bigger aspirations to global leadership. In that quest, once it has become a true democracy, it has joined hands with some of the least democratic regimes. Welcome to the world of diplomatic real-politic.