There is no guaranteed policy that can halt the Iranian nuclear program short of war, and even a military campaign may only delay Iran's acquisition of nuclear weapons capability. But U.S. policymaking regarding the Iranian nuclear issue inevitably boils down to a search for the least-bad option, and as potentially costly and risky as a preventive war against Iran would be, allowing Iran to acquire nuclear weapons could result in far heavier costs and risks.

The United States probably could deter Iran from a direct nuclear attack by threatening massive retaliation and the assured destruction of the Iranian regime, but there is lingering doubt that Iranian President Mahmoud Ahmadinejad, who reportedly harbors apocalyptic religious beliefs regarding the return of the Mahdi, would have the same cost-benefit calculus about a nuclear war that other leaders would have. Moreover, his regime might risk passing nuclear weapons off to terrorist surrogates in hopes of escaping retaliation for a nuclear surprise attack launched by an unknown attacker.

Even if Iran could be deterred from considering such attacks, an Iranian nuclear breakout would undermine the Nuclear Non-Proliferation Treaty and trigger a nuclear arms race in the Middle East that could lead Saudi Arabia, Egypt, Turkey, Iraq and Algeria to seek to build or acquire their own nuclear weapons. Each new nuclear power would multiply the risks and uncertainties in an already volatile region.

Iran also might be emboldened to step up its support for terrorism and subversion, calculating that its nuclear capability would deter a military response. An Iranian miscalculation could easily lead to a military clash with the United States or an American ally that would impose exponentially higher costs than would be imposed by a war with a non-nuclear Iran. All of these risks must be considered before deciding on how to proceed if diplomacy fails to prevent the prospect of a nuclear Iran.

Preventing a nuclear Iran is one of the most difficult and dangerous problems that will confront the incoming administration of President-elect Barack Obama. After he takes office on Jan. 20, Obama should learn from the experience of past efforts to negotiate with Iran and deal with Tehran from a position of strength, stressing sticks rather than carrots, because for Iran, a nuclear weapon is the biggest carrot.

Targeted economic sanctions and the possible use of military force will be Obama's biggest sources of leverage. The only hope of aborting the Iranian nuclear bomb lies in convincing Iran's leaders that the economic, diplomatic and possible military costs of continuing their nuclear program are so high that they threaten the regime's hold on power. Any talks with Iran should be structured to produce quick results and preclude Tehran from stretching out the negotiations indefinitely.

Obama also should rule out a presidential meeting with Iranian leaders until they have agreed to end their nuclear weapons efforts in a verifiable manner based on intrusive international inspections. Accepting anything less will only give Iran's radical regime yet another opportunity to renege on their commitments when it suits their purposes.

James Phillips is research fellow for Middle Eastern affairs in the Douglas and Sarah Allison Center for Foreign Policy Studies, a division of the Heritage Foundation's Kathryn and Shelby Cullom Davis Institute for International Studies. Peter Brookes is senior fellow for National Security Affairs in the Davis Institute at The Heritage Foundation.