Iran has begun publicly preparing for a possible U.S. attack, as tensions mount between the Bush administration and this country's hard-line leaders over Tehran's purported nuclear weapons program.

"Iran would respond within 15 minutes to any attack by the United States or any other country," an Iranian official close to the conservative clerics who run the country's security and military apparatus said on condition of anonymity.

The Tehran government has announced efforts to bolster and mobilize recruits in its citizens' militia and is making plans to engage in the type of "asymmetrical" warfare that has bogged down U.S. troops in neighboring Iraq, officials and analysts say.

Iran insists it needs nuclear technology to meet its burgeoning domestic energy requirements and bolster its scientific community. But the United States accuses it of using nuclear energy as a fig leaf for a weapons program.

"Iran remains the world's primary state sponsor of terror, pursuing nuclear weapons while depriving its people of the freedom they seek and deserve," President Bush said in his State of the Union address earlier this month.

France, Great Britain and Germany, also suspicious of Iran's nuclear ambitions, have insisted on strict inspections and have urged Iran to give up components of its nuclear program, specifically its effort to establish what is called the nuclear fuel cycle, lest it provoke a military attack.

Fuel cycle technology has peaceful applications -- energy production and medicine, for example -- but it is also viewed as the foundation for weapons development.

The United States has criticized the approach taken by Europe and the International Atomic Energy Agency, the U.N. nuclear watchdog agency, as too soft on Iran. Generally, however, Bush administration officials insist they support European diplomatic efforts, but refuse to rule out military options if Iran refuses to acknowledge and give up its alleged pursuit of weapons of mass destruction.

The Pentagon recently revealed that, as a matter of routine preparedness, it had upgraded its Iranian war plans, and the Washington Post has reported that unmanned U.S. drones have been flying over suspected nuclear sites in Iran.

Iranian authorities, too, say they have been getting ready for a possible attack. Newspapers have announced efforts to increase the number of the country's 7 million-strong "Basiji" volunteer militia, which was deployed in human-wave attacks during the Iran-Iraq war in the 1980s. Iranian military authorities have paraded long-range North Korean-designed Shahab missiles before television cameras.

The Iranian military also is attempting to give the impression that it is bolstering its conventional forces. In December, it staged a massive war game -- deploying 120,000 troops as well as tanks, helicopters and armored vehicles near its western border with Iraq. More recently, Iran's press reported that the Iranian air force had received orders to engage any plane that violates Iranian airspace, just after the reports emerged of U.S. spy planes monitoring Iran's skies.

One Western military expert based in Tehran said Iran was sharpening its abilities to wage a guerrilla war. "Over the last year, they've developed their tactics of 'asymmetrical' war, which would aim not at resisting a penetration of foreign forces, but to then use them on the ground to all kinds of harmful effect," he said, on condition of anonymity.

It remains unclear how much of the recent military activity amounts to a mobilization and how much is propaganda. Iranian officials and analysts have said they want to highlight the potential costs of an attack on Iran to raise the stakes for U.S. officials considering an assault and to frighten a war- weary American public.

"Right now it's a psychological war," said Nasser Hadian, a University of Tehran political science professor who recently returned from a three-year stint as a scholar at New York's Columbia University.

"If America decides to attack, the only ones who could stop it are Iranians," he said. "Pressure from other countries and inside America is important, but it won't prevent an attack. The only thing that will prevent an attack is that if America knows it will pay a heavy price."

Iran's army includes 350,000 active-duty soldiers and 220,000 conscripts. Its elite Revolutionary Guards number 120,000, many of them draftees. Its navy and air force total 70,000 men. The armed forces have about 2,000 tanks, 300 combat aircraft, three submarines, hundreds of helicopters and at least a dozen Russian-made Scud missile launchers of the type Saddam Hussein used against Israel during the 1991 Gulf War. Iran also has an undetermined number of Shahab missiles that have a range of more than 1,500 miles.

Yet both outside military experts and Iranians concede that the country's antiquated conventional hardware, worn down by years of U.S. and European sanctions, would be little match for the high-tech wizardry of the United States.

"Most of Iran's military equipment is aging or second-rate, and much of it is worn," Anthony Cordesman, a military expert at the Center for Strategic and International Studies (CSIS) in Washington, wrote in a December 2004 assessment of Iran's military.

The Western military expert said he spotted 30-year-old American-made M113 armored vehicles at recent military demonstration in the northwestern city of Qazvin. "Those tanks were able to go a few meters in front of us," he said. "But in a combat situation? I don't know."

Despite the state of its equipment, Iran could create myriad troubles for the United States and the world.

Its security forces include a number of intelligence agencies with extensive overseas experience and assets, experts say. Iran's highly classified Quds forces, which answer directly to Iran's spiritual leader, Grand Ayatollah Ali Khamenei, are believed to have operations in Lebanon, the Palestinian territories, Jordan, Afghanistan, Pakistan, India, Turkey, the Persian Gulf region, Central Asia, North Africa, Europe and North America, according to a December 2004 report prepared by CSIS.

Within minutes of any attack, Iran's air and sea forces could threaten oil shipments in the Persian Gulf as well as the Gulf of Oman. Iran controls the northern coast of the Strait of Hormuz, the narrow waterway through which oil tankers must navigate, and could sink ships, mine sea routes or bomb oil platforms, according to the CSIS report.

Iran could activate Hezbollah militants in Lebanon, whom it supports, to launch attacks on Israel. It could have operatives attack U.S. interests in Azerbaijan, Central Asia or Turkey.

"Iran can escalate the war," said Hadian. "It's not going to be all that hard to target U.S. forces in these countries."

But most analysts agree that Iran's biggest trump card would be to unleash havoc in neighboring Iraq, where Shiites who spent years in Iran as exiles are assuming control of the government.

Although the Bush administration charges that Tehran already has been interfering in Iraq, many Iranians brush off the low-level infiltration as minor compared to the damage it could cause by allowing Iraqi militiamen to take heavy weapons into Iran, by backing the most extreme Islamist groups instead of the moderates it now supports, or by dispatching operatives across the long, porous border between the two countries.

Any Iranian retaliation "would surely start with attempts to mobilize Shia partisans in Iraq to try to turn the Iraqi south into an extension of the insurgency in the Sunni triangle," Gary Sick, professor of Middle East studies at Columbia University and former National Security Council adviser to then President Jimmy Carter, told a congressional panel last week.

Iraqi officials, wary of their country becoming a battleground for the conflicting ambitions of Tehran and Washington, concede the damage Iran could do in their country, which now hosts 150,000 U.S. troops.

"If Iran wanted, it could make Iraq a hell for the United States," Hamid al-Bayati, Iraq's deputy foreign minister, said recently.

© 2005 San Francisco Chronicle

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