WASHINGTON — This past week, I announced my decision to support the nuclear weapons limitation agreement reached between the major world powers and Iran.

In my years of public service, I’ve never faced a more difficult decision – the stakes are high, the issues complex and the risks difficult to calculate.

But after carefully reading the agreement, attending multiple hearings and classified briefings, and discussing it in depth with my colleagues, foreign ambassadors and experts both outside and inside the Obama administration, I have concluded that it is in the best interest of the United States and our partners and allies in the region to approve the deal, as our international partners have already done. Here’s why.

First, if the deal is implemented effectively – and implementation will be crucial – it will prevent Iran from achieving a nuclear weapon for at least 15 years.

Second, at the end of those 15 years, if we take the right steps, we will still have essentially the same options we have today to prevent Iran from developing a bomb.

And third, if this agreement is rejected, then the likely alternatives are either unrealistic or downright dangerous.

It’s important to understand what this deal does: It places strong and explicit restrictions on Iran’s nuclear program for the first 10 to 15 years, including a substantial rollback of its stockpile of enriched uranium, strict limits on further enrichment and effective dismantling of its plutonium route to a nuclear weapon.

Many detractors argue that, although the deal curbs Iran’s nuclear capability, it still positions that country to become a nuclear threshold state after 10 to 15 years. That’s a possibility that we need to be prepared for – but the truth is that Iran is a nuclear threshold state right now and can achieve a bomb within two to three months.

If this agreement is implemented properly, Iran’s nuclear capabilities would be curbed to the point where that breakout period would be extended to at least one year for at least a decade and probably more.

The deal also contains stringent inspection and verification provisions that provide us with a high level of confidence that, should Iran try to pursue a bomb, the international community would catch them.

Under the terms of the deal, the International Atomic Energy Agency will be able to inspect any known nuclear site at any time, and U.S. intelligence agencies, along with their international counterparts, will also closely monitor Iran’s activities.

If a previously unknown nuclear site is discovered, the IAEA can request access to it within 24 days – longer than I would have liked, but well before Iran could cover up the presence of radioactive nuclear materials.

I can’t argue – nor can anyone – that this deal is perfect. For example, I would have preferred the limits extended past 15 years and that the U.N. arms embargoes would remain in place indefinitely.

But we also have to ask ourselves: If we reject this agreement, what happens next? I’ve heard opponents suggest that walking away and reimposing or strengthening the sanctions could bring Iran back to the table to get a better deal.

But that argument doesn’t account for the fact that the other major world powers that have joined us in implementing those sanctions have already approved this deal – and our unilateral rejection would almost certainly lead to the erosion of those sanctions. And if that happens, we are left with the worst of all worlds: an Iran unfettered by the terms of the agreement and subject to a weaker sanctions regime.

At that point, if Iran moves toward a bomb, our remaining option is military action – but a strike would only set the Iranian nuclear program back a few years, and could require additional strikes at an unpredictable and incalculable cost. Clearly, this should only be the option of last resort.

This is a hard call; there are risks either way. But in the end, the crucial question is not whether this is a perfect deal, but whether it is better than the likely alternatives. In my judgment, it is clearly so, and our country, the region and the world will be the safer from the threat of a nuclear Iran because of it.