This week, the U.N. Security Council faces one of the most crucial tests in its history as it begins deliberating Iran’s nuclear ambitions. As President Bush said once under different circumstances, the council may now turn into a debating society or a serious player in world affairs.

Yesterday in Tehran, a Foreign Ministry spokesman, Hamid Reza Asefi, said Moscow’s offer to establish a Russian-Iranian joint project for uranium enrichment on Russian soil “is no longer on our agenda.” The mullahs seem intent on confrontation with the rest of the world, but until now the U.N. system was unable to face the challenge, relying on futile diplomacy and false hopes for compromise.

There are alternatives. America could bypass the United Nations by gathering a “coalition of the willing” – this time prominently featuring France – that will impose sanctions on Iran even without approval by the council. And if all else fails, as a former Israeli army chief of staff, Moshe Yaalon, told the Hudson Institute last week, Israel has the military means to slow the mullahs’ nuclear race.

“Deja vu,” Russia’s foreign minister, Sergei Lavrov, said on a Turtle Bay visit last week. Formerly a U.N. ambassador, the cigarette-smoking, Scotch-loving, sharp-tongued Mr. Lavrov led his country’s diplomacy on the eve of the Iraq war, when the Security Council reached a glorious standstill. The attempt to rein in America backfired, and in the process the United Nations became irrelevant.

“We are the reason the cold war remained cold,” a senior Turtle Bay official boasted to me last week. In fact, mutually assured destruction was what kept the Soviets and the West from annihilating each other. The sanity of MAD is, however, lost on Iran, a champion of suicide bombers.

Ambassadors of the council’s five permanent members – America, Russia, China, Britain, and France – met twice last week in an attempt to coalesce behind a fairly benign statement calling on the mullahs to obey the International Atomic Energy Agency and asking the IAEA to report in two weeks or a month on Iran’s cooperation.

The rest of the council will consider the proposed statement today and for the rest of the week. The negotiations will revolve around key phrases like “decides.” Diplomats friendly to Iran will try to avoid any use of that word, which indicates future action against Iran. Those friends of Iran – which after yesterday may or may not include Russia – also will want to prevent the council from instituting a monthly report by the IAEA director, Mohamed ElBaradei.

On Wednesday, investigator Serge Brammertz is expected to report to the council his findings regarding the assassination of a former prime minister, Rafik Hariri. Top Syrian officials might be implicated and even the Baathists’ defenders on the council might agree to act against them. In the case of Sudan, the Security Council, despite numerous meetings and pronouncements, has been unable to stop genocide.

As for Iran, although Foreign Minister Manouchehr Mottaki said yesterday that it will not use the petroleum weapon, withdrawing Iranian oil from the market and prompting the world price to rise, many on the council fear that exerting sanctions on Tehran might inevitably lead to oil at $100 a barrel. The case, as Secretary of State Rice said last week, is also at the top of Washington’s foreign agenda.

Then there is the elephant in the room. Mr. Yaalon’s speech in Washington was heavily criticized by Israeli officials, but it did little more than restate their policy: While the threatened Jewish state will rely on world diplomacy as long as possible, it will not allow Iran to obtain nuclear weapons. Mr. Yaalon merely hinted at means, like submarine-launched missiles, and said that Israel has the hardware to deal with the expected Iranian retaliation.

For months, Americans and Europeans concerned about Iran urged referral to the Security Council. If the council fails to act now, Iran will not necessarily escape punishment. But for the United Nations, which has been declining in influence since the Iraq war, this last chance might really prove to be the final one.