This week, the country has been focused on the “nuclear option” in the U.S. Senate. But Americans should be focused on a more literal nuclear option: whether Iran will continue pursuing the know-how to build nukes.

At a fascinating hearing held last week by the Senate Foreign Relations Committee, experts agreed there were no good options for preventing an Iranian bomb.

Sen. Richard Lugar, R-Ind., displayed the frustrations provoked by the Iran issue when he plaintively asked: “Is there hope of a solution leading to no Iranian nuclear weapons? Can anyone offer a glimmer of hope?”

A little background on why this issue is so perplexing: Iran insists its nuclear program is peaceful, as permitted under the Nuclear Nonproliferation Treaty. But Tehran hid its nuclear activities for more than 18 years, and nuclear fuel can be diverted for weapons.

To avoid punitive measures, Iran agreed with the United Kingdom, Germany and France (the so-called EU-3) to suspend work on developing a nuclear fuel cycle. The Europeans, backed by the Bush administration, are trying to persuade Iran to abandon its fuel-enrichment program in return for small economic rewards. But Iran is balking.

Why is it so risky if Iran gets the bomb? With its history of support for radical groups such as Hezbollah and Hamas, many worry that Iran might pass a nuclear weapon to terrorists. True, Tehran would face terrible retribution if it did so, but, in Iran, political factions often operate independently of the government. The Carnegie Endowment’s nuclear expert George Perkovich noted: “If they (Iran) acquire nuclear capacity, who controls it?” Some radical Iranian faction might decide to share nuclear information or materiel with a terrorist group.

Yet the options available to prevent Iran’s acquisition of nukes are all extremely iffy.

First is the Regime Change Option: the hope that Iran’s regime will implode. This hope was dismissed by the expert witnesses. Despite widespread Iranian unhappiness with the regime, the population has no appetite for bloody revolution and no serious opposition leaders. Political change will surely happen, but not soon.

Next comes the Military Option: bombing Iran’s nuclear facilities. Vice President Cheney even suggested that Israel “might decide to act first” if others failed to end Iran’s program. But unlike the Iraqi plutonium reactor that Israel bombed in 1981, Iran’s uranium enrichment program can be dispersed and hidden. Bombs might delay, but not end, the program. The Nixon Center’s Geoffrey Kemp told the committee that the net effect of a military campaign against Iran “would be to reinforce Iran’s determination to get nuclear weapons.”

Moreover, the United States cannot afford to enrage Iran if it wants stability in neighboring Iraq and Afghanistan. Iranian Foreign Minister Kamal Kharrazi just visited Iraq, where officials made clear they want good relations with Iran. In an interview in January, before he became Iraqi prime minister, Ibrahim al-Jaafari told me the United States should clarify to Iran (and Syria) that “the U.S. presence (in Iraq) does not mean a threat to them.”

So if force won’t work, and regime change isn’t in the offing, what can persuade Iran to change course? The present U.S. strategy is to support the EU-3 negotiations from the background. Should Iran unfreeze its uranium-enrichment program, U.S. officials want to pursue the Sanctions Option at the U.N. Security Council, with European support.

If the entire Security Council backed really tough economic sanctions, Iran might waver. But there is small chance that Russia or China will abandon energy interests in Iran and support sanctions. And U.S. efforts will be hampered by memories of cooked intelligence on Iraq.

Which brings me to the one glimmer of hope at the hearing. Call it the Freeze Option. If sanctions won’t work, the only default option may be buying time.

Iranian officials have indicated they might continue the freeze on their program if the economic rewards were greater. The witnesses at the hearing agreed the EU-3 talks wouldn’t succeed unless the incentives for Iran were bigger.

Nicholas Burns, undersecretary of state for political affairs, told the committee that there was “no reason to believe that economic incentives … would make a real difference.” But why not let the Europeans make an offer? And why not signal to Iran, as Jaafari suggested, that we are not out for regime change (which we can’t engineer anyway), although we will support any Iranian democratic reformers?

In the long run, Iran’s system is bound to change from the inside. It will change faster if Iraq stabilizes, which requires Iran’s cooperation. If we can achieve an Iranian nuclear freeze for a couple of years while the country ferments, that’s better than a failed effort at confrontation.

There are really only two Iran options: a freeze or learning to live with the Iranian bomb.