Hundreds of thousands of people have been demonstrating in the streets of Tehran this week, and perhaps in other Iranian cities as well. Because of a government news blackout of the demonstrations, we simply don't have very much information. Much of what we do know comes from the crowds who have been text-messaging each other as well as the outside world, and the use of amateur cell-phone videos.

What we see is what the demonstrators have sent us. The crowds are young; indeed more than 50 percent of Iranians are under 25. So far, the Iranian government seems at a loss, refusing to accept the demands of the protesters for new elections, but also unable to stop the demonstrations, at least without massive bloodshed. This is the greatest Iranian crisis in 30 years, when the shah was deposed and the Ayatollah Khomeini returned from exile to create the Islamic Republic.

It is clear that a titanic struggle is under way for the future of the country. Islam itself is not an issue, as some of those leading the crowds are ardent Muslims themselves. The crisis has moved beyond a dispute over election results to a struggle over the balance of power in the country and Iran's future orientation. There is a deepening split in the country's governing elite and institutions. On the one hand are the religious, social and political conservatives, who fear rapid social change and cling to an angry confrontation with the West, especially over nuclear issues. They include the supreme leader, Ayatollah Ali Khamenei, President Mahmoud Ahmadinejad, and much of the religious and military establishment. They would seem to be invincible, and yet they are not. The conservatives remember only too well the crowds of students and others in the streets of Tehran in 1979 that brought down the shah, who also seemed invincible as he controlled the more obvious levers of power. Indeed, many elderly clerics, including the supreme leader himself, were instrumental in the move to get rid of the shah and install the Ayatollah Khomeini.

On the other hand are the reformers, whose principal leader at the moment is former Prime Minister Mir Hossein Mousavi. He is no flaming liberal, and at one time was a political and social conservative. But he is well remembered for his adroit handling of the Iranian economy in the 1980s, and in his subsequent years out of office as an architect and professor, he seems to have mellowed.

Moreover, he is married to Zahra Rahnavard, the popular former chancellor of Alzahra University and a close adviser to former President Mohammad Khatami, a definite reformist, whose many attempts at political and social reform were thwarted by the ultra-conservative Guardian Council, the body that is Iran's political, religious and social watchdog. They have banned many of the country's principal reformers from standing for office.

The principal thing to note about Mousavi is that while he supports Iran's nuclear program — indeed, he virtually began it — he appears willing to discuss it with the West and perhaps come to some sort of compromise. That alone makes him deeply suspect in the eyes of the hardliners, especially Ahmadinejad. There is also a lot of discontent over the economy and the country's tenuous living standards. The economic situation alone makes Mousavi attractive to middle-class voters. Moreover, there is a growing discontent among women — the majority of voters — about restrictions placed upon them by an increasingly religious and conservative government.

Ahmadinejad, however, appeals to the poor and the religiously conservative. We need to bear in mind that it is entirely possible that Ahmadinejad actually won the June 12 election. What has called the results into question is the super-swift government counting of the vote that gave Ahmadinejad a two-thirds majority, even in such places as Tabriz, Mousavi's hometown. That would be like President Barack Obama losing the African American vote. Possible? Yes. Likely? No.

Mousavi insists upon a brand-new election and no mere partial recount as offered by the supreme leader. He is determined to avoid the kind of provocation that could bring down on the crowds in the streets — and on himself as well — the full force of the government. That force is formidable, especially the 125,000-member Revolutionary Guard and its auxiliary, the Basij militia, both defenders of the Islamic revolution. On the other hand, it is not known whether these forces would actually fire upon their fellow citizens.

There are many possible outcomes from the present crisis, which is why it is essential for Obama to move carefully. So far he has resisted the siren calls from our own conservatives to rally overtly behind the Iranian demonstrators. That is precisely what he must not do until matters are clarified. At the end of the day, he must deal with whatever government is in power.

Bill Stewart, a former Foreign Service officer and correspondent for Time magazine, lives in Santa Fe.