Iran's president-elect may have been a leader of the mob that took American diplomats hostage in Tehran in 1979. Or not. We don't know for sure. And that is the most intriguing aspect of this very Persian tale.

Mahmoud Ahmadinejad has tepidly denied the accusations of six ex-hostages that he interrogated and threatened them and others. He flicked the charges away as "only rumors." Other Iranian revolutionaries who were at the embassy say that he was not.

But a photograph from that era shows an urban guerrilla who looks very much like a younger version of Ahmadinejad escorting an American prisoner. The Bush administration sees enough to launch an inquiry and has promised to get back to us.

In Iranian terms, the new president's low-key demurrals would resemble George Washington letting controversy hang over "rumors" that he crossed the Delaware or Mao Zedong hedging about his role in the Long March. Ahmadinejad is not likely to measure up to those leadership models, but the event in question is that formative.

The siege of the U.S. Embassy in Tehran is the cornerstone of the Iranian revolution and the continuing conflicts of the Persian Gulf. Even more than the overthrow of the regime of Shah Mohammad Reza Pahlavi in February 1979, the embassy takeover nine months later set in concrete the clerical character of the regime and the radical path it still follows. And a photograph of a handshake was key to that drama as well.

After admitting the exiled and mortally ill Iranian monarch to the United States that October, the Carter administration was confident it could balance the move by reaching out to the technocrats and politicians who had come to power with the ayatollahs in Tehran.

National security adviser Zbigniew Brzezinski went to Algiers for a handshake with Mehdi Bazargan that was to quickly cost the Iranian prime minister his job and help set the embassy takeover in motion. Radicals who had been protesting the shah's admission to the United States seized on photographs of the Nov. 1 handshake to whip up fury at the embassy, bring down Bazargan and banish the first set of "moderates" from the government. (They were to resurface in the Iran-contra scandal.) If Ahmadinejad, a practicing politician, could claim any shred of a connection to that punch to the chops of the Great Satan, he would presumably exult in it. But he sidesteps both the honor and the indignity of it all.

Modesty? Unlikely from this populist demagogue, who won by promising the moon, sun and stars to Iran's poor. Desire for international respectability in his new office? Not much sign of that either. On its face, Ahmadinejad's sparse denial rings true, or true enough when it comes to politics in the Middle East. What may ultimately be more important is that he isn't going out of his way to gild his hard-line credentials or to antagonize the United States over any role he might have had in the embassy seizure.

His victory also has reverse spin on it: It clarifies the political situation in Iran. There is no longer pretense or hope that secretly pro-Western "moderates" influence the government there. Ahmadinejad's promises commit the ayatollahs and friends to delivering the prosperity that Mohammad Khatami's outgoing administration never could. Disappointments must be brought to the hard-liners' doorstep next time.

If Iranians must now deal with the regime as it is, so must the rest of the world. It exists and is coherent. There is no point in pretending its legitimacy depends on Washington's attitude toward the regime, as the Bush administration has done. In dealing with the regime's nuclear ambitions and its strong influence in Iraq, the world must take into account Iran's legitimate security interests.

But Iran's cheating on nuclear weapons and its support for Middle Eastern terrorism have to be taken into account and dealt with as well. Europeans who wanted to encourage "the moderates" by granting carrots to Tehran have lost the horse they hoped to ride in the ongoing negotiations on Iran's nuclear program.

That means neither surrendering to despair nor launching an invasion. Instead, it means engaging in an extended contest of wills with an adversary intent on giving up little and gaining much. By clarifying the situation, Ahmadinejad makes it easier for the world to come to terms with what the regime in Tehran really is -- and perhaps for the regime to come to terms with itself.