Iran is providing a premature and very high-risk test of President Barack Obama's new approach to American diplomacy.

Simplified, the thesis of the new Obama approach is that if the United States plays nicer with others, others will play nicer with us and be more willing to help do tough things.

I've never held out much hope for the Obama approach. I believe that nations generally act in their self-interest without regard to sentiments about other countries.

On the other hand, the Bush administration's blustery approach only made the rest of the world more hostile and resentful, which wasn't in our self-interest. So, it was worth giving the Obama approach a whirl.

The Obama approach, however, was intended to generate good will over time. The United States would cooperate more on international issues such as climate change and in international organizations such as the U.N. We would engage in direct diplomacy with troublesome regimes such as in Iran, North Korea, Syria, Venezuela and Cuba, all of which Obama said would receive presidential meetings in his first year in office.

After showing good will and willingness to engage in direct diplomacy, the rest of the world would be more willing to support the United States if tougher efforts to rein in dangerous rogue behavior nevertheless proved necessary, went the theory.

Iran has spoiled and short-circuited the rollout of the new Obama diplomacy. The disputed Iranian election made it difficult to engage in direct diplomacy with the current government without appearing to give the back of the hand to those risking their lives to protest its illegitimacy. Iranian President Mahmoud Ahmadinejad stepped up his attacks on Israel's right to exist. And Iran remains unflinching and deceitful about its rapidly-developing nuclear program.

So, the Obama administration is going to have to test its new diplomatic approach before laying all the prerequisites by trying to organize strong sanctions against Iran. It increased the stakes for such diplomacy greatly by abandoning the missile defense complex in Poland at least in part, it seems clear, to induce greater cooperation on Iran by Russia.

Sanctions would have to be crippling to have any hope of forcing Iran to abandon its nuclear ambitions. Only the equivalent of a non-military embargo on gasoline imports is thought to have sufficient effect to possibly get the job done.

To be effective, a ban on Iranian gasoline imports would require extraordinary international cooperation. Western powers might adopt them, and indeed Western suppliers have already been cutting ties to Iran. But gasoline is transportable and tradable, so masking its origins is difficult but doable.

The national interest calculations would suggest that Russia and China are unlikely to go along with potentially effective sanctions against Iran, officially or unofficially. Iran is a client of Russia's on nuclear technology and military apparatus. China is a client for Iranian oil, which provides 15 percent of China's crude supplies.

They also have the interest Robert Kagan has cited that all autocratic regimes have in thwarting efforts to pressure and delegitimize other autocratic regimes.

The need to very quickly cobble together an effective sanctions regimen against Iran is an unfair test of Obama's new approach. But it's the test that has to be taken.

If the effort to impose effective sanctions fails, as it is likely to do, the Russian gambit will prove very costly.

If sanctions fail and Israel doesn't act, the world may have to live with an Iran capable of producing a nuclear weapon. In that world, the Poland missile defense complex would have been very valuable.

The Obama administration said that it was abandoning the Poland complex designed to shoot down long-range missiles because the intelligence suggested Iran has slowed down the development of its long-range capability. It's hard to credit that. Iran has successfully tested a two-stage rocket and put a satellite in space.

Theater missile defense, which the Obama administration says it will emphasize more, is important. But in a world with a nuclear-capable Iran, so is the European missile defense against long-range threats the Obama administration just abandoned.