General John Abizaid, chief of the US Central Command, refused to discuss US military planning in response to a mounting confrontation with Iran over its nuclear program.

But in an hour-long session with defense reporters here, the commander of US forces in the region laid out capabilities Iran has that US military planners must reckon with.

"Number one, they have naval capacity to temporarily block the Straits of Hormuz, and interfere with global commerce if they should choose to do so," Abizaid said.

About 40 percent of the world's oil transits through the straits at the entrance to the Gulf. Shutting it down would cause world prices to skyrocket, analysts predict.

"Number two, they've got a substantial missile force that can do a lot of damage to our friends and partners in the region," he said.

"Number three, they have a pretty robust terrorist surrogate arm that could in the event of hostilities cause problems not only in the Middle East but globally.

"And number four, they have a very substantial land army that, while it's not offensively worrying, is certainly capable of conducting asymmetric warfare."

The Iranian army, for instance, is practicing how to carry out hit-and-run attacks on supply lines in enemy territory, he said.

Abizaid's comments came amid speculation in the US media that the United States may be beginning to prepare for war against Iran.

Time magazine reported this week that the US Navy's chief of operations, Admiral Michael Mullen, has ordered a review of the navy's plans for countering a blockade of the Strait of Hormuz.

It also said navy minesweepers, a submarine and an Aegis cruiser have been ordered to prepare to deploy in the Gulf, a possible sign of preparations.

Pentagon spokesmen said the military conducts contingency planning for all types of situations, but that the United States remains committed to diplomacy.

"That's not to say we are not going to do due diligence with respect to our capabilities," said a defense official. "That's just the way the military operates. We've got to make sure our capabilities are commensurate with our requirements."

The official, who spoke on condition of anonymity, said two of four minesweepers the Navy has permanently stationed in the Gulf are due to be decommissioned at the end of the year, and those are likely to be replaced.

But the lack of progress on the diplomatic front has fueled debate over how to respond to the prospect of a nuclear-armed Iran.

"In my opinion, the Iranians are trying to achieve a nuclear breakthrough for military purposes. That's how I read the intelligence," Abizaid said.

"It's my opinion that won't happen for some years, but it's also my opinion that if Iran becomes a nuclear power, it so destabilizes the region that it makes it more dangerous for everybody, to include the Iranians," he said.

While he would not comment on US military preparations, Abizaid said he is holding ground forces in reserve in the Gulf and Kuwait as a hedge against "unforeseen problems that may arise from for example ... Iraq, or Iran."

With 147,000 US troops in Iraq, the US army and marines are stretched thin. But Abizaid warned Monday in an interview with CNN that underestimating US air and naval power in the region would be a "dreadful mistake."

"Right now Iran is the most powerful military force in the region, except for the United States of America," Abizaid said Tuesday. Abizaid said he did not count Israel, generally believed to have the most capable military in the Middle East, because it does not fall in his area of operations.

"But the mismatch between our military power and their military power is very, very substantial," he added.

Nevertheless, he said, Iran should not be underestimated.

"Its conventional forces are defensively oriented but its intelligence force are offensively oriented," he said. "And so Iran has traditionally conducted an asymmetric campaign in the region. And they continue to do that."

Iran has strengthened surrogates like Hezbollah with sophisticated new weapons, he said, citing anti-tank weapons, anti-ship cruise missiles and longer range missiles used against Israeli forces in Lebanon.

A new armor-busting rocket-propelled grenade believed to be of Iranian origin has turned up in Iraq after first making an appearance in Lebanon, in what could be a "hint about things to come," Abizaid said.

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