If an air and missile strike could destroy Iran's nuclear weapons program, it might seem the best of many bad options. But the likely costs outweigh the benefits.

Is the intelligence on Iran so much better than it was on Iraq? The Clinton administration launched Operation Desert Fox against Iraq in 1998 to degrade its weapons programs, and even today we don't know what it achieved. As President Clinton later put it, "We might have gotten it all; we might have gotten half of it; we might have gotten none of it. But we didn't know."

Would Desert Fox II in Iran, even on a larger scale, produce a very different result? The Pentagon can hit facilities it can see with relative confidence. But much of Iran's program is underground, and some of it we don't know about. Even if a strike set back Iran's plans, we would not know by how much. For all the price we would pay, we wouldn't even know what we'd achieved.

And we would pay a price. President Mahmoud Ahmadinejad and the mullahs would declare victory, as Saddam Hussein did in 1998, and probably would gain some sympathy and admiration from the Muslim world and beyond. Instead of pushing for sanctions against Iran at the U.N. Security Council, the administration might be fending off resolutions censuring it for "aggression."

Then there is the prospect of Iranian retaliation: terrorist attacks, military activity in Iraq, attempts to close off the Persian Gulf shipping lanes and disrupt oil supplies. Unless we were prepared to escalate, ultimately to the point of taking down the regime, we could end up in worse shape than when we began.

But the inadequacy of the military strike option does not mean we can simply turn to diplomacy. Diplomacy by itself has no better chance of success. The present Iranian regime appears committed to acquiring a nuclear weapon. It has been undeterred by the prospect of international isolation or economic sanctions and apparently deems these hardships an acceptable cost. If so, even bigger carrots will not persuade it to forgo a program it considers vital to its interests. Fear of U.S. military action is probably the only reason Iran even pretended to negotiate with the Europeans (and a big reason why the Europeans have negotiated with Iran), but it has not been enough to stop their program.

We need to reorient our strategy. Our justifiable fixation on preventing Iran from getting the bomb has somehow kept us from pursuing a more fundamental and more essential goal: political change in Iran. We need to start supporting liberal and democratic change for an Iranian population that we know seeks both.

No one wants to see Iran get a bomb, but it does matter who is in power. We don't worry that France or Great Britain has nuclear weapons. We tolerate India's and Israel's arsenals largely because we have some faith that their democratic governments will not use them. Were Iran ruled by even an imperfect democratic government, we would be much less concerned about its weaponry. It might dismantle its program voluntarily, as did Ukraine and South Africa. But even if it didn't, a liberal and democratic Iran would be less paranoid about its security and therefore less reliant on nuclear weapons to defend itself.

The Bush administration, despite its doctrine of democratization, has not yet tried to apply it in the one place where ideals and strategic interest most clearly intersect. It has done little to push for political change or to exploit the evident weaknesses in the mullahs' regime. The steps are obvious: Communicate directly to Iran's very westernized population, through radio, the Internet and other media; organize international support for unions and human rights and other civic groups, as well as religious groups that oppose the regime; provide covert support to those willing to use it; and impose sanctions, not so much to stop the nuclear program -- since they probably won't -- but to squeeze the business elite that supports the regime.

Some worry about sparking another Hungarian-style uprising or Tiananmen Square massacre. True, the mullahs might quash dissident movements we support, just as they have quashed dissident movements we did not support. But the Iranian people would not be worse off than they are now, and if some want to risk their lives for freedom, who are we to tell them they shouldn't?

This doesn't mean giving up on diplomacy. A strategy aimed at changing the Iranian regime is entirely compatible with ongoing diplomatic efforts to slow Iran's weapons programs. It might even aid diplomacy, since Iran's leaders fear internal unrest more than external pressure. In the 1970s and '80s, the West pursued arms control while it supported dissidents and liberalization in the Soviet bloc. The one did not preclude the other.

But we shouldn't delude ourselves. Efforts to foment political change won't necessarily bear fruit in time to prevent Iran from acquiring a bomb. That may be the risk we have to take. But if this or the next administration decides it is too dangerous to wait for political change, then the answer will have to be an invasion, not merely an air and missile strike, to put an end to Iran's nuclear program as well as to its regime. If Iran's possession of a nuclear weapon is truly intolerable, that is the only military answer.

The nonmilitary answer in Iran is political change. That is where we should now be directing our energy, our diplomacy, our intelligence and our substantial economic resources. Yes, time is growing short, and partly because so many years have already been squandered. But better to start now than to squander more.

Robert Kagan, a senior associate at the Carnegie Endowment for International Peace and transatlantic fellow at the German Marshall Fund, writes a monthly column for The Post.