It was a blunt exchange with the bitter bite of the ideological battles between talk-show hosts Keith Olbermann and Bill O’Reilly — except the sparring partners were Hillary Rodham Clinton and Iran’s supreme leader, Ali Khamenei.

“We see that the government of Iran, the supreme leader, the president, the Parliament, are being supplanted, and that Iran is moving toward a military dictatorship,” snapped the U.S. secretary of state while visiting Qatar last week. In Tehran, Ayatollah Khamenei snarled back: “Now the Americans, once again, have dispatched their agent as a saleswoman to the Persian Gulf to spread lies.”

That’s a far cry from the policy of engaging Iran that President Obama pursued so hopefully when he took office (although administration officials insist their door is still open). At a moment when the U.N. nuclear agency is suggesting, for the first time, that Iran is seeking nuclear-weapons capability, does Obama have a coherent strategy toward Tehran?

Engagement worth a shot

I think it made sense to try engagement, even though the odds were daunting. Obama sent warm messages to the Iranian public and two letters to Khamenei offering to reset relations. The ayatollah didn’t answer. Perhaps anti-Americanism is too essential to the regime’s worldview.

We’ll never know what might have been had Iran’s rulers not rigged the June elections and provoked the country’s most serious political unrest since the revolution. The leadership is now so deeply divided that it’s unlikely to revamp its nuclear policy or relations with the “Great Satan.” The Revolutionary Guards — an aggressive military force that controls much of Iran’s economy, along with its nuclear and foreign policies — seem to be calling the shots.

In such circumstances, the White House had no choice but to activate Plan B: pursuit of harsher international sanctions to curb Iran’s nuclear program. But, having offered engagement, Obama has a better chance of getting U.N. Security Council members on board.

“They can’t say this administration didn’t open the door,” said Nicholas Burns, who worked on the Iran issue as undersecretary of state in the last Bush administration. “Now Obama is in a much stronger position to say, ‘Those guys wouldn’t meet us at the table.’ He has a lot more authority.”

Yet, even if Russia agrees to new sanctions (a possibility) and China acquiesces (more iffy), many experts ask whether sanctions will change the regime’s behavior.

True, Iran’s economy is in difficult straits. But, says Mark Fowler, a former CIA officer who leads Booz Allen Hamilton’s Persia House research service, Iranian officials “are pretty well set up to weather sanctions, pretty good at working around them, and at smuggling. It’s a question of how much pain you can bear, and they can bear a lot.”

Sanctions would indeed worsen Iran’s economic problems, says Suzanne Maloney, an expert on Iran at the Brookings Institution, but “the difficulty is to connect the impact with a reversal of positions by Iranian authorities.” To the extent that sanctions target the Revolutionary Guards, Maloney said, their impact will be “much more powerful. But they won’t be a knockout punch.”

And just about everyone I’ve talked to doubts that congressional sanctions against refined oil products would make a difference. The idea sounds good, since Iran has insufficient refineries to produce much of its gasoline. But such sanctions are likely to hit the public hardest, while the Revolutionary Guards profit from smuggling rackets that evade the ban. Moreover, the regime, which is trying to reduce government subsidies for gasoline, could then blame sanctions, rather than its own mismanagement, for the public’s pain.

Sanctions the best option

Yet, with all these caveats, sanctions are the best option at present. A military attack would rally Iranians around the regime without ending the nuclear program. (Unlike Iraq’s Osirak reactor, which Israel bombed in 1981, Iran’s program is dispersed, with much of it deep underground.) An attack would also risk the unforeseen consequences of another Mideast war, including skyrocketing oil prices.

Sanctions buy time to isolate the regime internationally for its human rights abuses and for its violation of U.N. resolutions on its nuclear program. They buy time to strengthen the defenses of Iran’s Gulf neighbors. They buy time to wait out possible political changes inside Iran and to see if Iran’s leadership will reconsider compromise. Finally, they buy time to prepare a containment strategy, should all else fail.

And we have time: Despite its bluster, Iran is having serious technical problems with its nuclear program. And experts doubt that its leaders have decided whether to produce weapons or just go to the brink of doing so. (Khamenei insisted again earlier this month that Islam forbids such weapons.)

The Revolutionary Guards, who pursue earthly power rather than apocalyptic dreams, are unlikely to risk Tehran’s destruction by testing a nuclear weapon or launching one at Israel or the West. Their worldly interests may ultimately lead to an internal split between diehards and pragmatists who seek to join the global community.

If sanctions don’t produce quick results, Obama will have to withstand political pressure from those who want military action. “This is a long-term chess match, and we’ve only seen the opening moves,” Burns said. This game will take a steady hand.

— Trudy Rubin is a columnist for the Philadelphia Inquirer. trubin@phillynews.com