BOSTON — At the Group of 20 summit in Pittsburgh, President Barack Obama locked arms with the leaders of France and the United Kingdom to warn Iran that it must immediately halt its nuclear program.

Obama accused Iran of building a secret nuclear fuel plant in violation of the U.N.-mandated oversight and said that Tehran had posed a “direct challenge” to the international community.

In the city of bridges, Obama essentially threatened Iran that it has just burned one too many with the international community.

But in choosing to do so on the public stage of Pittsburgh’s G20 summit with all the world’s media watching and looking for any story more interesting than a long-winded communique on the economy, Obama was essentially doing what he does best.

That is, public diplomacy. And, as always, his tone is pretty close to perfect. He sounded firm, convincing and respectfully multilateral, and that tone goes a long way to swooning the world. It gets people around the globe to believe that the real America is rational and a natural leader in a dangerous world. This is a decidedly different image from the unilateral and seemingly belligerent America put forward by President George W. Bush. But former diplomats and Middle East analysts believe Obama will need more than perfect pitch in the public diplomacy of Iran, which interlocks directly with the profound policy challenges on Afghanistan, Iraq and the wider goal of global nuclear non-proliferation.

This is chess on many levels, not pop music.

To succeed in bringing Iran to halt its nuclear program and conform with the U.N. watchdog on nuclear proliferation, he will have to do the much harder diplomatic work of bringing China and Russia fully on board.

That won’t be easy as China and Russia do not believe sanctions will work, and as closer neighbors to Iran they have practical economic interests in Iran.

If Obama does not accomplish that real diplomacy, the confrontation of words with Iran will turn into a stand-off. And, if history is a judge, Iran will ultimately wait that out.

In neighboring Iraq, Saddam Hussein did just that for many years at the turn of this decade.

In the mid- to late-1990s, Saddam played the cat-and-mouse game with the U.N. inspectors.

And it is sobering to remember that that game along with the events of Sept. 11 served as a triggering mechanism for Bush’s flawed and ill-fated invasion of Iraq in 2003.

The U.S.-led offensive toppled Saddam’s brutal regime and ended all questions — real or fabricated — of weapons of mass destruction there, yes, but it also dragged the U.S. into a conflict where it has paid heavily in “blood and treasure,” as they say in the military.

Obama accused Iran of “breaking the rules that all nations must follow” and demanded that U.N. inspectors must immediately be permitted to inspect the nuclear facility.

“It is time for Iran to act immediately to restore confidence of the international community by fulfilling its international obligations,” Obama said.

Tehran apparently tried to preempt this steely determination on the part of Washington, London and Paris by communicating with the U.N. nuclear watchdog agency that it had a second uranium enrichment plan under construction.

But few were buying it.

French President Nicolas Sarkozy said Iran was going down a “dangerous” path and threatened stepped-up sanctions on Iran if it did not comply.

British Prime Minister Gordon Brown said that Iran’s violation of the International Atomic Energy Agency’s regulations should stiffen the resolve of the international community to draw “a line in the sand” against Tehran.

But there are many who questions whether even sanctions will work with Iran. William Luers, a 30-year career diplomat for the U.S. State Department who served in several postings as ambassador and recently stepped down as president of the United Nations Association, has joined with other top former ambassadors to urge dialogue with Iran.

Luers is the author of a recent memo on Iran for the White House and Thursday night he attended a dinner along with several dozen former diplomats and analysts with Iranian President Mahmoud Ahmadinejad.

“He is a dreadful person, but he was unusually agreeable last night,” said Luers, hastening to add, “What we know this morning casts new light on his gentility.”

But even if Ahmadenijad seems to go out of his way to make it difficult for Obama to stick to his previously stated willingness to open dialogue with Iran, Luers and other diplomats believe the Obama administration, in the long run, is wise to go with that initial instinct.

“No matter what problems we have with an enemy, you have got to talk with them,” said Luers, who is now a visiting lecturer at Tufts University for the Project on Justice in Times of Transition.

Not so much for altruistic reasons, he says, but because it is the only practical path forward.

The most difficult foreign policy challenges this administration faces are Afghanistan, Iraq and nuclear proliferation. And all three have one thing in common: Iran. It neighbors both Iraq and Afghanistan and it clearly needs to come into the fold of the international community on its nuclear program.

“We think sanctions will not achieve the ends of getting Iran to change its behavior. And the idea of using military force, the ultimate sanction, is a very dangerous path. We simply do not have the ability to open a new front in the Middle East.”

“To open dialogue with Iran is a big leap for Americans,” said Luers, and after the events of this morning it’s understandable if it seems to Americans like a jump off a bridge.

But, he added, Obama and Secretary of State Hillary Clinton will need to step up the administration’s diplomatic game. They will have to do the long math on engagement with Iran and the hard work of solving an intricate equation in which Iran is a variable for the most serious foreign policy issues the U.S. faces.

Editor's note: This column has been updated to reflect the fact that Obama is working toward a wider goal of nuclear non-proliferation.