We know quite a bit about Iran’s nuclear program, and what we know is not encouraging.

Iran is reported to be enriching uranium at two sites – some of it to levels of 20 percent, far beyond what is required for civilian purposes. The International Atomic Energy Agency also reports that Iran is carrying out research to develop designs for nuclear warheads. In short, Iranian officials’ claims that their nuclear program is aimed solely at power generation or medical research lacks all plausibility.

Yet there is still much that the world does not know. For example, we do not know whether Iran is conducting secret activities at undisclosed sites, or when Iran could develop a crude nuclear weapon, with estimates ranging from several months to several years. We also do not know whether Iran’s divided leadership has decided to develop nuclear weapons, or to stop just short, calculating that the country could derive many of the benefits of possessing nuclear weapons without running the risks or incurring the costs of actually doing so.

Either way, Iran’s activities confront the world with difficult choices. None is costless or risk-free. Moreover, neither the costs nor the risks are possible to calculate with precision.

One option would be to accept and live with a nuclear or near-nuclear Iran. This assumes that Iran could be deterred from using its weapons, much as the Soviet Union was during the Cold War. Missile defenses could be expanded; the United States could extend security guarantees so that Iran would understand that the threat or use of nuclear weapons would be met with a decisive American response.

But there are significant drawbacks to acquiescing to a nuclear-armed Iran. Given its use of subversion and terrorism against its adversaries, a nuclear-armed Iran might be even more assertive. It might also transfer nuclear-related material, technology, or weapons to allies (Hugo Chavez’s Venezuela, for example) or militant organizations such as Hezbollah and Hamas. And rather than promoting caution and stability in the region, Iran or Israel could be tempted to strike first in a crisis.

Nor can it be assumed that Iran’s divided and radical leadership would always act rationally, or that proliferation would stop with the Islamic Republic. If Iran develops its nuclear weapons, countries such as Saudi Arabia, Turkey and Egypt would be tempted to purchase or develop nuclear weapons of their own. A Middle East with multiple fingers on multiple triggers is as good a definition of a nightmare as there is.

At the opposite end of the spectrum of policy choices is a preventive attack: a military strike (most likely by Israel, the U.S., or both) against sites in Iran associated with its nuclear program. The core objective would be to interrupt the emergence of a threat that is still gathering.

Here, again, there are considerable drawbacks. Even a successful preventive attack would at most set back Iran’s nuclear program a few years. It would almost certainly be rebuilt, presumably in underground, fortified sites that would make future attacks far more difficult to carry out.

Moreover, Iran could well retaliate immediately against targets that could include Saudi Arabia, Iraq, Afghanistan and U.S. interests worldwide – as well as sites on American territory. Hezbollah could attack Israel. If all of this happened, the price of oil would skyrocket owing to shortages and fears, possibly driving much of the world economy, already in a precarious position, into recession. An armed attack could also cause the Iranian public to rally around the government, reducing the chances that a more responsible leadership might emerge.

It thus comes as little surprise that the United States and much of the world have explored alternatives, including regime change in Iran. But, however desirable that might be, no policy can assuredly bring it about.

As a result, the principal policy toward Iran centers on the imposition of increasingly painful economic sanctions. The rationale underlying this policy is that Iran’s leaders, fearful of losing political control as popular discontent increases over the sanctions’ effects, will recalculate the costs and benefits of their nuclear activities and become receptive to negotiated constraints in exchange for removal of sanctions.

That could happen. International support for sanctions is considerable and increasing. It is becoming more difficult for Iran (whose economy depends to a large extent on oil exports of more than 2 million barrels a day) to find customers – and especially customers willing to pay full price. Meanwhile, Iran’s currency is weakening, pricing imported goods out of many Iranians’ reach.

Additional elements of current policy that seem to be having an effect are clandestine efforts aimed at impeding Iran’s ability to import sensitive technologies. Viruses have infiltrated computers in Iran, reducing the efficiency of the centrifuges central to enriching uranium. It is also possible that the assassination of selected individuals has slowed the advance of Iranian nuclear efforts.

But slowing Iran’s efforts is not the same as stopping them. So one question is whether existing sanctions can be extended and tightened; here, China and Russia must determine their priorities. Another question is whether any sanctions will be enough to persuade Iran’s leaders to accept verifiable limits on their nuclear program. And a third unsettled issue is how long Israel or the U.S. will tolerate Iranian efforts before striking militarily.

Indeed, the only certainty may be that Iran’s nuclear program will be a major international issue in 2012 – quite possibly the most important one.

Richard N. Haass, formerly director of policy planning in the U.S. State Department, is president of the Council on Foreign Relations. THE DAILY STAR publishes this commentary in collaboration with Project Syndicate © (www.project-syndicate.org).