Tehran's disclosure that it is building a second uranium enrichment plant near the holy city of Qum has derailed the Obama administration's already faltering efforts to engage with Iran. The United States will now cling even more tightly to the futile hope that international pressure and domestic instability will induce major changes in Iranian decision-making.

Indeed, the meeting on Thursday in Geneva of the United Nations Security Council's five permanent members and Germany with Iran (the "five plus one" talks) will not be an occasion for strategic discussion but for delivering an ultimatum: Iran will have to agree to pre-emptive limitations on its nuclear program or face what Secretary of State Hillary Clinton calls "crippling" sanctions.

However, based on conversations we've had in recent days with senior Iranian officials -- including President Mahmoud Ahmadinejad -- we believe it is highly unlikely Iran will accept this ultimatum. It is also unlikely that Russia and China will support sanctions that come anywhere near crippling Iran. After this all-too-predictable scenario has played out, the Obama administration will be left, as a consequence of its own weakness and vacillation, with extremely poor choices for dealing with Iran.

Because President Obama assembled a national security team that, for the most part, did not share his early vision for American-Iranian rapprochement, his administration never built a strong public case for engagement. The prospect of engagement is still treated largely as a channel for "rewarding" positive Iranian actions and "punishing" problematic behavior -- precisely what Mr. Obama, as a presidential candidate, criticized so eloquently about President George W. Bush's approach.

At the United Nations General Assembly last week, President Obama used language reminiscent of Mr. Bush's "axis of evil" to identify Iran and North Korea as the main threats to international peace and vowed to hold them "accountable." In Geneva, we can expect the United States to demand that Iran not only accept "concrete" limitations on further nuclear development but also demonstrate the peaceful nature of its nuclear program to avoid severe sanctions.

This approach prompted Mr. Ahmadinejad, during a meeting last week, to declare that Iran does not believe Americans are "serious" about strategic cooperation. He argued that, when Iran had previously agreed to limit its nuclear development -- as when it suspended uranium enrichment from 2003 to 2005 -- Western powers offered nothing in return, and instead sought to "restrict our rights even further."

This was more than a diplomatic failure by the West -- it was also a serious blow to the credibility of reform-minded politicians in Iran. Is it a surprise, then, that no candidate in Iran's recent presidential election supported renewed unilateral restrictions on its nuclear program? Mr. Ahmadinejad has now reiterated that it should be possible to cooperate with Washington to resolve the nuclear issue, but only in the context of a broader strategic understanding -- something the Obama administration has not accepted.

Absent some agreement with Washington on its long-term goals, Iran's national security strategy will continue emphasizing "asymmetric" defense against perceived American encirclement. Over several years, officials in both the reformist government of Mohammad Khatami and the conservative Ahmadinejad administration have told us that this defensive strategy includes cultivating ties to political forces and militias in other states in the region, developing Iran's missile capacity (as underscored by this weekend's tests of medium-range missiles), and pushing the limits of Tehran's nonproliferation obligations to the point where it would be seen as having the ability and ingredients to make fission weapons. It seems hardly a coincidence that Iran is accused of having started the Qum lab in 2005 -- precisely when Tehran had concluded that suspending enrichment had failed to diminish American hostility.

American officials tend to play down Iranian concerns about American intentions, citing public messages from President Obama to Ayatollah Ali Khamenei, Iran's supreme leader, as proof of the administration's diplomatic seriousness. But Tehran saw these messages as attempts to circumvent Iran's president - another iteration, in a pattern dating from Ronald Reagan's Iran-Contra scandal, of American administrations trying to create channels to Iranian "moderates" rather than dealing with the Islamic Republic as a system. President Ahmadinejad underscored this point to us by noting that Mr. Obama never responded to his congratulatory letter after the 2008 United States election -- which, he emphasized, was "unprecedented" and "not easy to get done" in Iran.

The Obama administration's lack of diplomatic seriousness goes beyond clumsy tactics; it reflects an inadequate understanding of the strategic necessity of constructive American-Iranian relations. If an American president believed that such a relationship was profoundly in our national interests -- as President Richard Nixon judged a diplomatic opening to China -- he would demonstrate acceptance of the Islamic Republic, even as problematic Iranian behavior continued in the near term.

After taking office in 1969, Nixon directed the C.I.A. to stop covert operations in Tibet and ordered the Navy to stop its regular patrols of the Taiwan Strait even while China was supplying weapons to kill American soldiers in Vietnam. President Obama has had several opportunities to send analogous signals to Tehran - such as ending Bush-era covert programs against Iran -- but has punted.

Unfortunately, the Obama administration was enticed by the prospect of regime-toppling instability in the aftermath of Iran's presidential election this summer. But compared to past upheavals in the Islamic Republic's 30-year history -- the forced exile of a president, the assassination of another, the eight-year war with Iraq and the precipitous replacement of Ayatollah Khomeini's first designated successor, Ayatollah Hussein Ali Montazeri, with Ayatollah Khamenei -- the controversy over this year's election was hardly a cataclysmic event.

Furthermore - and notwithstanding the comment by President Dmitri Medvedev of Russia that sanctions are "sometimes inevitable" -- the Obama administration's focus on mustering support for effective economic penalties is delusional. For three years, Moscow has given just enough on sanctions to keep the nuclear issue before the Security Council, because Russian officials calculate that is the best way to constrain unilateral American action. But Russia has consistently watered down any sanctions actually authorized. Senior Russian diplomats continue to say that Moscow has not agreed to support any specific additional measures. Moscow may well acquiesce to a marginal expansion of existing sanctions, but it will not accept substantial costs to its own economic and strategic interests by supporting significantly tougher steps.

China may also agree to a marginal expansion of existing sanctions, but will not endorse measures that hurt important Chinese interests. An Obama administration proposal that Saudi Arabia "replace" the oil China now imports from Iran completely misreads Beijing's energy security calculus.

China is not only continuing to buy large amounts of Iranian oil, Chinese energy companies are also now developing substantial investment positions there -- justifiably confident that Washington will not sanction Chinese firms over energy investments in Iran. Chinese military officials are particularly focused on the potential for Iranian hydrocarbons to come to China through pipelines running across Central Asia, rather than through seaborne routes vulnerable to American naval interdiction. Iran is the only Persian Gulf country that can offer China such diversification of supply sources and transit routes.

The Obama administration may hope that even an ineffective quest for "crippling" sanctions will hold the line against those in Washington and elsewhere advocating a military strike on Iran's weapons program. That is sadly reminiscent of our experiences at the State Department and the National Security Council in the Bush administration, when officials who opposed the Iraq war championed "smart sanctions" and tighter containment of Saddam Hussein's regime as the alternative course. Such calls did nothing to change Mr. Hussein's calculations, and were overwhelmed by the exaggerated allegations of Iraq's renewed efforts to build nuclear weapons.

Instead of pushing the falsehood that sanctions will give America leverage in Iranian decision-making -- a strategy that will end either in frustration or war -- the administration should seek a strategic realignment with Iran as thoroughgoing as that effected by Nixon with China. This would require Washington to take steps, up front, to assure Tehran that rapprochement would serve Iran's strategic needs.

On that basis, America and Iran would forge a comprehensive framework for security as well as economic cooperation -- something that Washington has never allowed the five-plus-one group to propose. Within that framework, the international community would work with Iran to develop its civil nuclear program, including fuel cycle activities on Iranian soil, in a transparent manner rather than demanding that Tehran prove a negative -- that it's not developing weapons. A cooperative approach would not demonize Iran for political relationships with Hamas and Hezbollah, but would elicit Tehran's commitment to work toward peaceful resolutions of regional conflicts.