WASHINGTON — When Iran was caught last September building a secret, underground nuclear enrichment plant at a military base near the city of Qum, the country’s leaders insisted they had no other choice. With its nuclear facilities under constant threat of attack, they said, only a fool would leave them out in the open.

So imagine the surprise of international inspectors almost two weeks ago when they watched as Iran moved nearly its entire stockpile of low-enriched nuclear fuel to an above-ground plant. It was as if, one official noted, a bull’s-eye had been painted on it.

Why take such a huge risk?

That mystery is the subject of fervent debate among many who are trying to decode Iran’s intentions. The theories run from the bizarre to the mundane: Under one, Iran is actually taunting the Israelis to strike first. Under another, it is simply escalating the confrontation with the West to win further concessions in negotiations. The simplest explanation, and the one that the Obama administration subscribes to, is that Iran has run short of suitable storage containers for radioactive fuel, so it had to move everything.

The debate reflects the depth of confusion about the intentions of a badly divided Iranian leadership. Since October, when Iran agreed in principle to ship much of its nuclear stockpile out of the country so that it could be converted to fuel for a medical reactor, there have been a series of unexplained actions. President Mahmoud Ahmadinejad has veered from hailing the deal to backing away from it. The country has declared that it will soon build 10 new enrichment plants — a number it does not have the capacity to carry out. It has declared that it has answered all the questions posed by inspectors about potential work on weapons; the inspectors say there have been no responses since mid-2008.