MANAMA, Bahrain - After weeks of conflicting responses, Iran abruptly said yesterday that it was ready to exchange uranium for nuclear fuel, the key demand of a U.N.-sponsored initiative to defuse global fears over its nuclear program.

The conditions laid out in comments from Iran's foreign minister, however, are unlikely to satisfy the United States and its allies as they prepare to discuss sanctions against Tehran at a meeting that could take place this week.

Iran's stockpile of uranium is at the heart of international concerns because it offers Iran a possible route to nuclear-weapons production if the material is enriched to higher levels. Tehran insists it wants to use the material only to produce fuel for power plants and other peaceful purposes.

Under a U.N. plan proposed in October and being pushed by the United States and five other world powers, Iran would ship most of its uranium - up to 2,600 pounds - abroad. It would be enriched in Russia, turned into fuel rods in France, and returned to power a research reactor in Tehran that produces medical isotopes.

The material in the fuel rods could not be further enriched, preventing Iran from using it to make weapons.

"We accepted the proposal in principle," Foreign Minister Manochehr Mottaki told reporters at a regional security conference in Bahrain.

In what is almost certain to be a deal breaker, however, he spoke of exchanging the material in phases rather than all at once, as the U.N. plan calls for. He said Iran had offered to make a first shipment of 880 pounds of enriched uranium.

Carrying it out in slow stages would leave Iran in control of enough uranium to make a bomb.

A senior Obama administration official said Mottaki's remarks appeared to fall short of demands.

"Iran's proposal today does not appear to be consistent with the fair and balanced draft agreement proposed by the IAEA in consultation with the United States, Russia, and France," the official said, speaking on condition of anonymity because the United States has yet to formulate an official response to the development.

Officials at the U.N. nuclear agency could not be reached for comment yesterday.

In another change to the plan, Iran wants to receive the fuel rods immediately in simultaneous exchanges for its uranium because it says it is worried that France or Russia could renege on the deal.

Another unanswered question is whether the uranium Iran is offering to exchange would be shipped out of the country or just left - perhaps under observation - within its borders in what would present another departure from the U.N. plan.

Mottaki suggested the exchanges take place on Iran's Kish island, in the Persian Gulf, but he did not clarify whether the uranium would leave Iranian soil.

"We gave a clear answer and we responded, and our answer was we accepted in principle but there were differences in the mechanism," he said yesterday.