Don't stop worrying about Iranian nukes just yet.

Iran's new pledge to halt its advance toward a nuclear arsenal is at best a gamble, more likely a deception. But the awful truth of our predicament (and, by "our," I mean the world's) is that we have no real choice but to swallow hard and make the best of it.

The obstacles to even this course are considerable. The Iranians have a long record of lies and coverups about their nuclear program. The Europeans, who negotiated the new accord, are too willing to see the bright side of ambiguity in order to preserve harmony and commerce. Meanwhile, the Bush administration has no Iranian policy, apart from a passive-aggressive yearning for "regime change," and so seems unwilling to take part in any talks at a moment when shrewd U.S. engagement might make a difference. (Given the administration's inter-term disarray, it might also be unable to focus on the subject.)

No wonder, then, that the Germans, French, and British joined forces with the European Union's high representative to hammer out an Iranian policy without America. They negotiated an agreement with Tehran on Nov. 14, held firm to resist a brazen attempt at Iranian backpedaling, and last Monday saw the International Atomic Energy Agency endorse the deal with only tepid caveats.

Under the agreement, Iran pledges to suspend all activities related to the enrichment and reprocessing of uranium—including importing, manufacturing, assembling, testing, or operating gas centrifuges—as well as all activities involving the separation of plutonium. The IAEA has installed cameras and other surveillance equipment at all known sites to monitor compliance.

A key phrase here is knownsites. U.S. officials suspect Iran has several unknown sites, possibly underground. A Paris-based exile group, the National Council of Resistance of Iran, has made this charge. Like many exile groups (remember Iraq?), the NCRI has a spotty record on such matters, but it's more accurate than most. For instance, it was NCRI exiles who supplied evidence that Iran was secretly enriching uranium at its Natanz facility—a charge that Iranian officials denied and then had to confess was true. Natanz is now under IAEA monitoring, but who knows what other secret sites there might be?

More than this, the accord contains a big, wide-open loophole. The document explicitly notes that Iran's suspension of uranium enrichment is a) temporary; and b) "a voluntary confidence-building measure, not a legal obligation."

On the first loophole, it's worth emphasizing that the IAEA's endorsement on Monday notes "with concern that Iran has continued enrichment related activities … up to 22 November 2004"—i.e., until just one week ago. This enrichment continued "in spite of the request made by the [IAEA's] Board in September that Iran immediately suspend all such activities." It is farfetched to believe that Iran's mullahs have undergone a dramatic change in heart, intent, or trustworthiness over the course of seven days.

The second loophole—that the cessation is voluntary, not mandated—means that if the Iranians resume enrichment, they could argue that neither the European Union nor the United States has the legal right to bring the matter before the U.N. Security Council, because they didn't really break a legal agreement.

It's fairly obvious that the Iranians signed this accord only because the IAEA was about to make its November report on whether Iran was complying with the longstanding nuclear Safeguard Agreement—and they knew that a negative finding would force the Security Council to bring up the question of economic sanctions. In the past month, the Iranians cleaned up their act—released records that the IAEA had demanded, screeched the centrifuges to a halt, allowed intrusive monitoring and inspections, and finally signed the accord with the Europeans.

As a result, the IAEA gave the Iranians a clean enough bill of health. The resolution noted the need for further investigations and allowed that the agency "is not yet in a position to conclude that there are no undeclared nuclear materials or activities in Iran." But as for the declared sites, materials, and activities—which are all that the Safeguard Agreement covers—the IAEA could only "welcome" Iran's forthrightness. No need, or grounds, for anyone to raise a fuss at the Security Council.